11. Curvy/Plus Sizes
Modifying The Block For Larger Sizes
For those of you experiencing some dismay because I wrote that my one piece block is principally suited to bust sizes between 80cm and 94cm, please don't panic. This site is designed principally for students and home sewists with some, but limited, pattern making experience. At larger sizes more understanding is needed to achieve a good fit and this gets somewhat technical so I don't recommend it unless you really, really understand the properties of stretch garments. You will still need to create the One Piece Block, but modify it as set out below … the content of which is somewhat long winded but I don't know any other way to present it. It's not an easy topic and again I don't recommend doing this unless you are really familiar with stretch fabrics and pattern making ... I'm still here to support your questions if you want to go that route!
If you aren't up to making your own plus sized one piece block, I also now have a very special plus sized block set in my shop which is designed specifically with one concept in mind ...
with increased size comes increased variation in shape!
... so what I've done is create a linear average set of PDF blocks based on underbust (82cm to 144cm) with built in adjustments for every imaginable variation in shape ... you simply select your size and the adjustments you need exactly as you would if you were doing all the manual changes that follow on this page. This system has been thoroughly tested for customised one piece blocks ... it has one distinct advantage ... it makes it easy for you to let me know which adjustments you used (via an anonymous Google form) so I can eventually calculate the distribution of shape among plus sizing and create a set of different shaped ready to wear blocks ... the Holy Grail for curvy people everywhere!
The Plus Size blocks (multishape blocks) come in ...
17 half increment sizes as usual
Underbust 82cm to 144cm
Bust/Underbust difference up to 25.5cm
Hips 101cm to 137cm
up to 25 degrees of pelvic tilt variation
up to 10 degrees of shoulder tilt
sway back from 0 to 8cm
built in guides for varying waist
built guides for varying crotch width
built in guides for bubble butt (extra length)
complete with instructions on how to use the tool
But What If I want To Do It the Long Way?
Well that's what this section is for ... and it's also a good idea to familiarise yourself with all these concepts if you're learning pattern making even if you don't do curvy sizes.
Few people really understand exactly what it means when I say with increased size comes increased variation in shape ... and that it's the underlying reason of why so few people offer plus sizing in ready to wear ... at least not with great success. As a pattern maker, when you look at larger sizes you will start to find that you have many people who look completely different in shape but have identical measurements across the essential indicators. To fit each of these clients would require a specialist block/sloper ... indeed in the much larger of the plus sizes for RTW you might find yourself requiring several blocks to be able to fit everyone ... and that's just not going to happen in any viable production situation.
Let me put this more simply ... a regular size 84cm bust (Australian size 12) will fit the majority of the population and you only need one shape to fit everyone in that sizing. Yet less than 2% of the population of Australia are over a 120cm bust ... making such sizing only commercially viable for the largest of producers or for specialists in plus sizes. Not seeing plus sizes in small to medium is not about being non-inclusive, it's about economic survival ... they simply cant have that much stock on the shelf in the hope that that 2% might walk through the door. But that's not all.
For that 2%, only around 25% of them will actually fit what you make because of the increased variation in shape. So when you get angry with someone not carrying a plus size, just try to remember you're asking them to go right out on a limb commercially to include something that more than likely won't fit perfectly anyway! This is nobody's fault, it's just the reality of demographics.
Add to this that very few fashion schools can teach the intricacies of fitting plus size shapes because they usually only have a few hours each week over 2 to 3 years to teach the basics of pattern making. Some might touch on the subject in tailoring but it's extremely rare to find a school with the resources and time to offer the extra education required. Heck most schools I know are dropping the hours dedicated to pattern making because they justify that this is now mostly done by computer programs .... programs that have a single fitting method that is utterly hopeless in most cases for plus sizes. Only 10% of fashion schools are even offering basic stretch fit pattern making courses even though stretch garments make up the majority of sales these days. So don't go blaming schools or students because people don't know how to make plus sizes .... it takes years of experience and that's unfortunately slowly disappearing from the work place.
Ok so let's be more specific ... by larger/curvy sizes I mean a measurement beyond around an underbust measurement of 84cm. You might be taller or bigger busted or much bigger hips or indeed your every measurement might be scaled up perfectly proportionally from a 5ft 6in size 8B only you are 6ft 4in tall and wear a 40D bra! Larger does not mean fatter. Larger means one or more measurements are larger than those that have a predictable shape with respect to size. Finding out what those shapes are is why I started the plus size multi-shape block research above!
So Let's get into it!
Lycra is widely loved by all because it curves and stretches and goes around things while still sitting flat on the body. No darting is generally needed and a simple curved side seam is all that's required to make it fit snugly all over. Right? Wrong! Stretch textiles have the capacity to absorb a certain amount of distortion and still fit correctly. The emphasis here is on a certain amount. This is why you do see bust darts on larger sizes. As the sizing gets larger, the amount we require the textile to distort also increases ... but the fabric hasn't changed, has it?
To illustrate my point let’s consider the humble shoulder strap (see the Basic Tanksuit, step 3, for a quick refresher). As the strap gets narrower, we generally need to shorten its length to maintain the same tension. When we add more weight to the end of that strap we stretch it further, meaning for the same final length we need to shorten it some more right? Wrong again. Lycra only stretches to a point before it doesn't stretch any further. But before it gets to that point it takes tension away from other areas causing a cascading effect of trouble if you go for the quick fix. How about making the strap wider? Sure now that's the clear and obvious second solution ... but it's not a simple scale up in width. A bust at 94cm will get by on 3cm, but at 40D for example we'd be looking at a width of 5.5cm for the same support tension. It's all about tension, remember. But at 5.5cm wide it will look very odd indeed. Anyone know the answer yet?
The clever student will point out that larger busts need a bra type support so why not add extra lining or fabric to the strap area to stiffen the fabric so it supports better. Yes this will work. You could line the strap (and indeed the whole bust area) with something like power net but the problem still exists in the rest of the garment ... all you've done is increase the rebound capacity of the strap and the rest of the garment is still the same ... resulting in a mass of ripples fanning out over the bust, or indeed under it if you use a bra structure. Not only that, but now we have a much more complex and more expensive garment to manufacture. The more complex the garment, the less size range it will suit and hence limit its potential market. How do we do this simply without chasing ourselves round in circles? How many home sewists that are, say a 42B, want to start learning bras and swimsuits both at the same time?
The clever student was half right to suggest stiffening the fabric with extra lining. The problem here is controlling the differing fabric tensions over the whole body and chasing ourselves round in circles trying to get the garment to sit flat afterwards. Of course you could carry the extra lining all over the whole body to keep the tension even but why not do something even simpler? What? Simply increase the weight of the textile from the standard 170-180sm to something heavier like 195gsm or even 210gsm. You might have to specially order it, but it means simpler construction, narrower straps, standard lining and a whole lot less ripples ... but most of all it means even and more predictable tension control over the whole body, thus easier patterns.
All the above should help to illustrate why fabric quality is so critical to pattern making, and why the same pattern can produce both successful garments and complete failures.
Generally there are four areas in which shape varies significantly as size increases. In order of significance they are...
Hips, bottom and legs
Waist: both front and back, plus sway
Bust: mostly by increased cup variation
Pelvic Tilt (covered generally in next chapter)
So shape quickly becomes infinitely variable.
Hips, Legs & Bottoms
For any particular size, the range in hip measurements for a woman is greater than any other measurement (for men it's the waist), and with it, the larger the hip measurement, the greater the amount of shape variation. For example, a 76cm waist will have a hip measurement of between 95.7cm and 111.4cm, 95% of the time. That's more than the 12% one might use for ease. But even if your hip measurement is precisely, say 100cm, there are so many ways the shape of your hips can be different from the stereotypical average that the patterns must change in order to fit correctly. So you can see how impossible ready-to-wear might be! See the illustration below. The red line represents the true hip line that most people use ... and shows why I prefer to use a lower measurement over the cheeks.
Figure A represents the stereotypical outline shape of most people. If you take a look at the table below you can get an idea of how many people in each size group are actually represented by this shape. What you will notice is that as you increase in size, fewer people within that group are actually represented by figure A.
Figure B represents what is referred to as squared hip. This is initially a distinct skeletal change that is mostly seen in taller North American women (it still occurs in all sizes and heights). I have no idea what caused this change but I have trouble finding it in any images going back further than the 70's. Squared hip is usually padded by a little bit of fat creating a nice smooth shape which tucks in quite quickly toward the waist (about 40%) or the waist is almost missing (60%). Keep in mind this is a hip condition ... similar effects can be caused by things like "muffin top", the ring of fat at the lower tummy which teenagers like to hang over the top of their hipster jeans.
Figure C is the bane of women worldwide. Referred to as jodhpur thighs it's really only of interest to swimwear because it's usually accompanied by a sagging in the outer edge of the bottom cheeks (about 85%). It can't really be hidden by swimwear but we can do things like raising the leg line to draw the eye away from it. We do however also need to extend the leg line further out over the bottom, or the angle of the cheeks will cause the garment to ride up. This is why you had such high leg lines with square back bottoms in the 1980's... jodhpurs were the issue of the decade in women's magazines... and so many women ‘suffered’ from this figure shape that all swimwear styles were designed to cater for it. In fact does anyone remember the soft cotton Lycra bodysuits with the press studs in the crotch? The leg line was often so high to look good for the bedroom that if you ever tried on your 10 year old jeans from the 70's you'd find an exposed patch of skin above the belt line! The absolute worst thing you can wear if you have jodhpurs is hipsters as these exaggerate the feature and look awful. So much for trying to be fashionable!
Figure D is where the inside thighs touch when standing straight with your knees together. It usually occurs because of and stays after pregnancy but can occur naturally in a person of any size. It's of significance to swimwear because it's associated with lower and closer together bottom cheeks (or better said; there is little to no natural valley between the cheeks. From a pattern making perspective you can open the cheeks a little with a concave centre back seam (best suited to smaller sizes) or go the complete opposite and create a convexed centre back seam and allow the garment to move further out over the cheeks (larger sizes that also have jodhpurs for example).
Figure E represents both jodhpurs and square hips together. While exaggerated in this image, many North American and African women are of this figure type.
Figure F represents both jodhpurs and touching thighs, more typical of European and Australian mothers.
Figure G is the trifecta and usually (honestly) is a weight issue, although it is possible to have all three and it not be a weight issue on much taller women... the taller you are the more likely you are to also have jodhpurs, although the less likely your thighs will touch because both your pelvis is bigger and you thighs are longer (then it's a simple matter of physics and mechanics).
The above table is based on a survey size of 5,706 women of assorted nationality. You can clearly see from the table that as size increases the percentage of people of figure type A decreases sharply. The most notable shape issue is jodhpurs … in sizes 14 and up you are more likely to have them than to not, with 88% of women size 16+ having this feature. Which must raise the question is it normal to have them, with the smaller sizes being the odd ones out? Square hips and inside thigh do increase with size but are not significant numerically in themselves until combined with jodhpurs. There was one instance in a size 8 in which both squared hips and inside thigh were present but not jodhpurs ... this was on a very odd shaped model so I've removed her from the statistics.
OK that’s a lot of technical stuff and numbers. What it should tell you is that as size increases, a lower square or hipster leg line is a bad idea yet that’s what most shops have on offer. Why? It’s because the larger sizes cater to all three conditions at the same time in order to sell more product. Too bad if you’re a size 16 or greater, they won’t give you a choice! Seriously though, the numbers show that designers should be catering to the jodhpur shape in larger sizes and ignoring the other two conditions ... this would mean higher leg lines, not lower leg lines ... but of course, that wouldn't be fashionable would it?
From a custom pattern making point of view the trick is to identify which conditions you or your client have and design the garment accordingly as described above. You are really looking at either ...
Raising the leg line at the side seam about 4-5cm and moving the leg line at the cheek further outward by 3-4cm. The amount really is arbitrary but increases proportionally with the extent of the jodhpur.
Creating a square leg line as directed in the 70's Square Leg Maillot and adding in a convex curve into the centre back seam as illustrated below by breaking the back panel below the waist into quarters. You rotate up the top section about 5 degrees and open the other two by 5 degrees creating a little extra vertical ease (centre image). You can also add in extra horizontal ease as illustrated in the right hand image
Front & Back Waist Issues
The waist line is one of the trickiest areas to work with in larger sizes. In most cases we're not talking about a simple scaled up body type, we're really dealing with minimising the appearance of a weight issue. No doubt most of you are familiar with what looks best as far as styles go (e.g.; avoiding horizontal stripes, etc.), but we're talking pattern making. As such there are only two things we can do. We can minimize the issue by not drawing attention to it and/or we can actually change the shape a small amount.
Changing tummy and waist shape is usually done by use of stiffer fabrics or linings. Obviously the less stretch left in the fabric the less negative ease you can use, so there is a trade-off between being squeezed flatter and actually being able to put on the garment. Sounds simple doesn't it? Just add in some more ease and stiffen the fabric even more? Wrong, there is a catch.
Let's presume we're a little flabby in the tummy area. Simply making the garment tighter isn't going to do much more than create a Michelin man effect ... the garment will try to even out the tension in the fabric naturally by falling into the soft spots and riding over the rolls that won't compress ... sorry if I'm not pulling punches here but I need to be clear. It does this because in spandex it's possible to distort localized areas all independently of each other ... it's not a stiff textile ... you can poke your finger into one place and literally just 2 inches away the fabric is unaffected. So you can't use spandex as a flattening textile.
So instead we have two other options ... control textiles and compression textiles. The latter, compression, is a textile similar to spandex except that it has a very high rebound modulus. This means it can stretch pretty similarly to standard swim/dance spandex but it requires much more force to get it there (3-8% negative ease depending on the mesh) So it's tight to get on but it's still quite easy ... but what it does is move around the soft tissue of the body until everything is an even tension ... you may have heard of it being called shapewear. It's often mesh like in appearance but doesn't need to be. Higher levels of compression are NOT a change in knitting technique, but mainly achieved by increasing thickness of the elastic core of the inlay-yarn. What this means is that they can still distort locally just as normal spandex can ... it doesn't hide rolls (well ok maybe a tiny bit better) but typically moves them to somewhere they can be squished up ... you can still see an uneven surface.
Control textiles are something entirely different. These are a very different bar knit technique. These are low stretch, high rebound textiles but they are linked across the entire surface of the textile so there is no localized distortion ... they are designed to be a flattening textile not a compression textile. They hide the lumps and bumps by being stiffer while still having a mild stretch ... the best know example of which is Powernet. Typically we use it at no more than 4% negative ease. So when we talk about controlling the lumps and bumps in tummies, we're talking about lining with textiles like Powernet.
The problem we have today is that very few people know the differences between control and compression and retailers frequently mix them up too. So perform your own poke and stretch tests or read the material data sheets from your wholesaler.
When you have more rebound power at the front than at the back what you'll notice is that the back obviously stretches much more than the front ... but more importantly your side seams are no longer at the halfway point ... ie; on the body your side seams have moved significantly towards the front. This is the problem with almost every swimwear brand that uses Powernet as a control layer. There is also another problem with this .... all the tension lines in the back panel are now completely messed up because they don't match the front block properly anymore. It's very common to see ripples emanating from the either end of the seam used to lock the Powernet in place ... these are called loading corners and they represent a single point at which the layers suddenly change how much they can stretch.
Some people will suggest the following fixes:
move the side seams backward on the panels
reducing negative ease in the front panel
increasing negative ease in the back panel
using more panels
using Powernet all the way around
combination of all/any of the above
Actually the solution to this problem is none of the above .... you need to use what we call a floating sleeve ... a compression and control layer that's attached only at the vertical ends (typically from under bust to leg holes) and will pull in smaller than the outer layer.
We need to go completely around the body with something of EQUAL rebound .... control fabrics and compression fabrics are very similar in rebound (modulus of elasticity) .... this is why I mentioned them both earlier lol ... thus we can create a pattern for them both at 4% negative ease that will stretch way more than two layers of just control fabric, so you can get into it ... you could even lower that negative ease to 3% if you wanted. The compression layer is what has the strength to hold the control layer in place without rippling, while still allowing you to get into it.
The outer layer can be lowered to 7-8% and you just stretch to fit when you attach the leg elastics. It's really that easy. In answer to who did this the first time successfully .... Gottex. Now it's copied by a few high end swimwear brands so I'm told, but still so many brands haven't worked it out yet. Wasn't that exciting?
But there is also another problem with varying fabric types and linings in the same garment. Because they each have differing rebound tensions they move differently. Sometimes this is desired, sometimes this is terrible. Using control fabrics is great for flattening tummies but slows things from moving in other directions too .... fore example, when you sit down and increase the length from center back waist to crotch that length has to come from somewhere or the garment gets eaten by ones’ bottom ... usually the garment rides inwards from the outer cheeks first and then gets eaten. Many designers don't line the back to allow it to stretch more because of this but then they just exaggerate the first problem. The trick is to balance the tensions correctly.
So how do we balance the tensions when deciding where to place side seams (or working with different tensions anywhere else for that matter)? Simple! Let's say you want to line the front with Powernet and the back with normal swimwear lining. Cut yourself a strip of fabric about a meter long and 10cm wide. Sew liner to one half and Powernet to the other and then stretch it. Lets say, you stretch the whole strip to 130cm. Measure the length of the swimwear lining half (should be around 75cm depending on the liner quality) and the Powernet half (around 55cm) and you'll soon see that the Powernet lining gives up 55:75 of the stretch of standard swimwear lining. This means if you are using 12% negative ease normally, you need to lessen the negative ease of the section lined with Powernet to 8.8% (12% x 55/75) ... or essentially you're moving the side seams backward 1.5cm each side on for a 100cm hip measurement. This needs to be done for the whole area lined with Powernet. That's quite a visual difference even if it doesn't seem like it at first. In this way the seams will all sit where you want them to sit and the garment also moves more predictably!
The above balances tensions correctly, but what if you want even more tummy control? Well really you're only option is to use control and compression textiles (shapewear), all the way around the back ... think of it as a stretchy corset. Of course you still need to let out the negative ease in both front and now back panels to the correct amount for the rebound of your textile. About the only other thing to consider is that you cannot do this with a design that drops below the waist at the back (or even a few centimeters above it) or the garment will simply gape open and all your efforts may be lost. Support netting (control and/or compression fabrics) requires full circumferential covering to be effective! Also remember that the garment will be stiffer and more difficult to get into even though it's actually a little larger in the tummy section. The image below shows theoretically how I'd modify the pattern (not the block) for use with full wrap round shapewear ...
The red shaded area represents the tummy we're trying to control or flatten. You'll note that the tummy area is below the leg line at the side seam on a standard block so I've chosen firstly to use a squarer leg line which is consistent with the style larger sizes prefer and require. The dashed red line represents the limit of the support netting (I don't like to use netting in the crotch because it tends to rise). The blocks on the right show how I've reduced the horizontal negative ease across the whole bottom half of the blocks and then blended it in to the side seam above the tummy area. I've also squared off the side seam a fraction at the leg line, to correct the leg line curve, rather than adjust the leg line itself. This is the theory.
OK, moving on ... so now you're aware that side seam position can affect the appearance of a garment at the waist and hips. But where should it sit for optimal aesthetics? Optimal is how the human eye expects to see things in nature because in nature everything is balanced. If you're carrying a heavy box in front of your body you will lean backward to balance. If you could defy gravity for a moment and not lean backward then everyone would look at you strangely. Have you ever noticed how actors lifting painted polystyrene rocks in old movies always look ridiculous when they throw them?
Well that heavy box is much like carrying weight on your tummy. Pregnant women, for example, lean much further back. Straightening the side seam to make it look like you're standing square, looks as odd as the actor with the rock. But it's not just the tummy we need to consider. With respect to waist we are also interested in sway and, on some people, a pad of fat that sits just on and below the back waist (hereinafter referred to politely as fuller lower back). Take a look at the illustration below. The top picture shows the side profile of the stereotypical figure.
If we are to divide the hip measurement in two when making the blocks, the side seam sits exactly half way on either side ... but if the majority of the measurement is in the front, then the side seam will appear more forward. Now a certain amount of forward is needed because straight obviously looks wrong, but too far forward looks obvious as well. The correct position is somewhere in between ... i.e.; the design 'accepts' the person is carrying weight on the tummy by allowing the seam to move forward, but not so much so that the concept of how much weight is accurately realised by the viewer ... it's a fine line. I tend to draw the side seam (sometimes even literally) on the body as you see on the images above ... what looks right to the eye. Then I measure how much is in front and how much is in the back ... let's say my client, who has a waist of 78cm, has 43cm in front and 35cm in the back. Now if we had left the seam at the halfway point of 39cm you can see that it would have been way too forward.
There is the argument that if you put the side seam exactly at visual optimum as shown on the illustrations then you are trying too hard to hide something and people will again notice. I don't necessarily subscribe to this as I did place the seam at what I considered to be aesthetic to me. This argument suggests that you bring the seam back to somewhere between optimum (43cm) and halfway (39cm) so that the human brain recognises that the extra 'weight' is fairly represented by a certain amount of 'distortion'. Personally I think I'm already doing this when I draw the line on the body so to do it again would just be silly ... but you can make up your own mind by drawing the optimum and the halfway lines on the body and then having a good look as you move around the body.
Ok so we know we might need to move the side seam backward or forward, but what about sway? How does that affect the pattern? Sway is two things. It's firstly the natural curvature of the spine (which varies from person to person) and secondly it's a result of arching back to carry extra weight (think pregnancy for example). Now because the spine is at the back of the body, no matter how much you arch, the length of the back doesn't change significantly (not usually more than 2-3%) ... but the length of the front does. If you've made a one piece block according to the instructions you will already accounted for most of this, but it might serve benefit to tweak a little extra length in to the front block at the waist line. How much? If you consider that this will mostly be required in conjunction with moving the side seam backwards you can kill two birds with one stone. By moving the side seam backward we need to make the front waist measurement wider and the back waist measurement smaller. When we make it wider the length of the side seam will shorten (until it's square up with the hips at least) ... thus we need to lengthen it a little to make it match the original measurement and hence the back panel. It won't be much but it will usually correspond to the extra length needed in the front block ... so I tend to let one dictate the other. Furthermore, the narrowing of the back waist measurement will cause a lengthening of the side seam so I chop a bit out of the back block height at the waist line to make it match the original side seam length once again ... the reverse of what we did at the front. The result is often a block/pattern which looks peculiar, but a garment which has far less ripples, especially when the person twists.
Ready to wear designers will ignore almost all of the above because first and foremost they need a garment that has shelf appeal ... one that sits flat by having the front and back panels match with an evenly placed side seam. They want you to try on the garment assuming that you'll miss the finer aesthetic details until well after purchase ... and they're right to do so because most people will! Custom swimwear designers need to heed the above strictly because although the person won't know why, this will be the most significant difference in the feel and look of the garment as the person moves. Don't underestimate it!
The Bigger Bust
Probably the single most difficult part to making a swimsuit is dealing with larger bust issues. I have covered this topic everywhere in which it relates to each specific issue but I think we need to link it all together and look at the issue as a whole. Now by larger bust I guess I'm really referring to anything more than a couple of sizes over the average ... and average is somewhere slightly on the B cup side of a C, so by larger bust we're thinking D/DD and higher ... no matter how many FFs and Gs and Ks there are (and there's lots) there's still hundreds more Bs and Cs.
In my personal opinion, I do not like underwires in swimwear. As mentioned previously they present a host of manufacturing and legal nightmares. If you don't need one you shouldn't use one. Many people in the D+ group do need them and should probably just side step this page altogether and go straight to the Bra section. By using an underwire we're going to get all the support and shaping we need for the bra without affecting the design process of the rest of the swimsuit. But for those who do not want an underwire but fall into the larger bust size category, where do we start?
Well to begin with we're going to need to draft a One-Piece Block. The instructions were designed to create a one piece with the appropriate darting for the average C cup body. There is a link to How to Calculate Darting for any bust size which you should do (or go back and re-do if you didn't before) if you have a larger (or smaller) bust than a C. This then builds in the correct bust shaping for a one piece. If you're wondering why I didn't include the bust dart calculations initially (it's there now) on the one piece page it's because the site is designed for students making ready to wear clothing ... most of which are 16-17 year old girls to whom a number is easier to work with than even more calculations. OK so that's the correct shaping amount ... what next?
The great thing about swimwear is we don't really need to consider adding extra length to the vertical to compensate for fuller bust volume as we would have done with non-stretch pattern design. It's pretty much already built into the block with the horizontal bust measurement ... if you think about slicing the body into lots of little horizontal slices and each stretching around the body you'll get an idea of where I'm going with this. The smart ones among you may realize that tensions will start to become uneven if this happens, and yes you are right. And you'd also be right if you mentioned that uneven tensions in the bust to shoulder strap area result in lots of nasty ripples. However a bigger bust should mean wider and tighter straps which usually compensate. Really in the cup range D-DD-E you shouldn't need to add any extra vertical height to the block at all. For each cup size over a DD/E you might want to start adding an extra 5mm per cup to the vertical. How? Well I do this after I've already calculated the dart width and drawn the block. I consider it to be tweaking rather than predictive pattern making. In the image below I've taken a block for a 12E and simply sliced along the bust line, opened it up 5mm, then found the centre line of dart and redrawn the dart so that the seam lines are an even length.
This should really be enough to create the correct shape, but there's another issue that I think we need to tie into this page ... support. A standard darted one-piece really isn't designed to give support and unless you're a self-supporting silicone E+ cup then you're going to need as much as you can get without the underwire. I usually recommend incorporating an Empire Line Design into the pattern because it reduces the horizontal dimension under the bust which offers added support. You can of course reduce this dimension by changing the side seam curve a little as illustrated below. I've rotated the dart out of the way first...
Of course you should take the same amount from both front and back side seams in order to keep the side seam square down the body. Just a centimetre or so from each seam should make a considerable difference to comfort. Again this is something I consider to be no more than tweaking the block a little. Something else I like to do on large bust blocks is to turn the side dart down to somewhere between 45 to 60 degrees from the bust line. The vertical dart below the bust provides the most support, but without an empire line or princess line in your design, about 60 degrees is the maximum you'll find to be aesthetically acceptable. See the illustration below. I've rotated the dart a full 60 degrees down from the bust line.
Another thing I do with the 60 degree dart is bring it back further from the bust point ... normally I might bring the dart back just centimetre or two, but when rotated down you can afford to, and should, take as much as 3-4cm. This allows for the bust to drop relative to the garment during movement without the bust dart, then, pointing to somewhere above the nipple ... creating the impression that the bust is sagging.
It would also be an idea to utilise a stiffer lining material or heavier weight outer fabric to help hold everything in place. Beyond this there really isn't a great deal you can do for the larger bust without an underwire.
If you followed my site 10 years ago you might remember my Lazy Person's section where people input their measurements to get a computer generated pattern. The data from over 20,000 people showed clearly there aren't as many larger busts on larger bodies as there are larger busts on smaller bodies ... this is completely contradictory to common sense and indicates perhaps that much larger bodies are either avoiding swimwear or simply not making their own ... or that breast surgery really is rapidly on the increase in the 25-40 year old population as stated on all the plastic surgery TV shows and magazines. Honestly I'm not sure what I think about this.
Below is a computer generated table of bra sizes based on all the data people entered into the Lazy Person's block section. You can clearly see the anomaly in the 6-10 EE-F area of the table ... surely one wouldn’t expect to see any tiny figures walking around with anything larger than D breasts, let alone EE-F. This does suggest breast implants to me. Now I know there are people out there with natural breasts of that size, but the relative percentage should still decrease with each increase in cup size ... instead the opposite has occurred. I had been suspecting this for some time and I'm assuming I may well have had a large number of visitors in this category … such people will have trouble buying swimwear off the shelf!! I have had many people write in and tell me that they know more women with larger cups when it comes to a small band size than they do smaller cups ... this may well be true for their relatively small sample size of a dozen or so friends in a specific community or racial group, however this site developed a sample size over 20,000 that fall within 1 deviation on at least 2/3rds of their measurements which shows otherwise. So those who believe natural larger cup sizes exist on smaller bands, you are right, but still not outside of normal percentages.