Yesterday we were asked about why we use 12% in the blocks.
There is something else I need to mention. As you know, different fabrics stretch different amounts. It's not the amount of stretch that determines our percentage of negative ease, but the rebound strength of the fabric. Different fabrics may well stretch to the same amount but can have different rebound strengths.
Rebound is non-linear ... it generally increases as you stretch the fabric. Some fabrics only slightly, some significantly. This is important to mention because when we create a garment we're looking for even tension everywhere on the body ... if one area isn't fitted as well as another then it may have more or less tension than elsewhere ... causing instability (the garment moves around during wear) or worse, ripples (the shear between areas of differing tension). Even tension is essential. When we create a pattern we need to look carefully at where that tension is going.
But there's more. When we create cut outs and straps we can change the rebound properties of the fabric. Rebound relies on other parts of the fabric holding everything back ... when you narrow a section you lower its rebound strength, meaning lower tension ... hence why we shorten straps. But when we shorten them we are asking our fabric for more stretch to get the same rebound ... that's called distortion, and distortion can also cause shear ripples (we stabilise it with elastic at the edges). Tension is a compromise.
If you don't understand tension you cannot create a stable garment, unless by luck. The key to even tension is always an accurate fit based on accurate measurements. Relying on the fabric's stretch properties to accommodate fit instead of deliberately planning an accurate fit is just inviting problems. In custom made swim or dance we get to adjust patterns based on measurements so fit is generally much better, presuming we have a good starting block or pattern that allows for adjusting shape and size.
The fastest way to know if a ready to wear pattern will be unstable, or a poor fit, is if it lacks bust darting. Not everyone is an A or B cup so the pattern designer is relying on the fabric's stretch to accommodate shape ... meaning they're expecting uneven tension (assuming they even understand tension in the first place) ... or, as I say, deliberately building in poor fit and instability because they either don't like or can't do darts. This isn't an opinion, it's a fact based on the laws of physics .... like it or not fabrics move from high tension to low tension ... elastic does the same (can you say hungry butt?).
How many times have you seen someone in a sewing group asking why they fall out of the bottom of a bikini top, or why their bust is being flattened, or how can they get more support, or why is there rippling between the bust, or why are their straps distorting, or why are there 45 degree ripples down the straps, or (my favourite) why is the arm hole gaping so badly. Notice the complete lack of bust darting that accompanies those very same questions? But if you tell them that they need a full bust adjustment/dart their reaction is typically that they don't want a dart as that ruins the aesthetic ... you mean compared to the huge gape at the arm hole? They want a perfect fit with none of the problems, but no darting. I call that cognitive dissonance ... or refusal to accept reality/laws of physics. Pick one, you can't have both unless you have minimal shape or the pattern piece is smaller than the shape it's trying to cover.
But it's more than this. Designers know their product fails frequently when they don't include darts, they know it as they read it every day too! Some will say they are giving the customer what they want ... well sure if they're all small busted, but they're not. So I don't buy that excuse unless you're also deliberately being non-inclusive ... more than 75% of the population requires darting to resolve the fit issues I've mentioned above ... you expect the majority to perform an FBA instead of expecting the minority to remove the dart ... the problems get worse and more difficult with increased size.
So I'm going to come out and say it straight for everyone to hear ...
If you're a designer that doesn't include darts as standard then you are deliberately being non-inclusive on both size and shape and it's time people complained about it.
Especially as it's such an easy thing to provide ... it took me seven hours to add and grade three additional cup size options to the teens blocks AND adjust all the optional guidelines to those cup sizes, not to mention changing the layout and labelling ... it's no real technical challenge for a pattern maker.
Today I've seen these same fitting questions above in several groups and not one word from any of the pattern sellers (I'm not calling them pattern makers anymore).
Fit matters, tension matters, darts matter ...