Gaping Low Backs

Why is my low back one piece swwimsuit gaping?

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Over the last few days I've seen several people talking about the back of their dance outfits gaping at the sides when they cut a really low back line. And two people talking about horizontal ripples appearing at the center back of their swimwsuits. Then today I was asked again about how to stop gaping at the back.

Ripples and gaping are both indications you have an issue with uneven tension in your garment. Below I've attached some photos of mild gaping (first five photos), mild horizontal rippling (next three photos) and lastly both together .... all of these are mild because no professional swimwear retailer is going to put out photos with severe gaping or ripples ... but believe me they exist ... and usually I see it when home sewists ask why it's happening to their garments. I want to help people understand why.

1. All these photos have something in common (besides the fact they're all low back garments).

2. All of them have a serious pattern design flaw.

3. The cause is the same in every photo, just that it manifests as either ripples or gaping because of another reason.

So what is it and how do we fix it? Hint: it isn't by putting a strap across the back to hold everything in place or by covering it with a bow! We want the garment to look like this style, but without the gaping or rippling.


Let's say we take a fully wrap around Tanksuit .... how we do the straps is totally irrelevant to stopping the problem and nothing to do with its cause and neither, really, is the elastic.

The top illustration represents a tanksuit at bust to waist to hips ... the hourglass. The waistline is the most significant line in a swimsuit because this is the narrowest circumference on the body ... a garment completely fitted at the waist cannot ride up or down and is ANCHORED in this location .... anchored meaning that other areas on the body use this line to hold one side of the tension.
All the photos above showing ripples or gaping have one thing in common .... 𝗧𝗵𝗲 𝗯𝗮𝗰𝗸 𝗹𝗶𝗻𝗲 𝗰𝘂𝘁𝘀 𝗮𝗹𝗹 𝘁𝗵𝗲 𝘄𝗮𝘆 𝗱𝗼𝘄𝗻 𝘁𝗼 𝘁𝗵𝗲 𝘄𝗮𝗶𝘀𝘁 𝗹𝗶𝗻𝗲 𝗼𝗿 𝘁𝗵𝗿𝗼𝘂𝗴𝗵 𝗶𝘁!

As you lower you back line to approach the waist line (olive coloured swimsuit), the fabric is still anchored all around the body and everything stays in place. There is a sudden appearance of ripples angled upwards along the elastic line as you get within about half an inch above the waist line ... the fabric is telling you it cant hold the tension across the upper front panel anymore (Joshua Hart eluded to this). Increasing elastic tensions will do nothing to fix this .... but intuitively people still try and make it worse

The second you lower the back line to exactly the waist line the horizontal ripples appear, first at the side seam level with the waist line, then closer to center back.

If you lower the back line slightly more to about half an inch below the waist line you'll see ripples concentrate at the CB on the back line and the edge of the back line starting to pull away from the body ... this has nothing to do with elastic being short or long, but because we've now cut the main anchor around the body in half ... stretch an elastic band and then cut it somewhere and watch it snap at you ... this is what happened .... only the elastic band is still held in place by the rest of the garment.

As we cut the back line lower and lower away from the waist line the garment pulls more and more away from the body and eventually actually starts to roll over ..... even if there's straps pulling it back to the shoulders, neck or to the other side .... its rolling over!!

Why? Because the horizontal tension above the waist has nothing anchoring it anymore ... nothing saying that it has to wrap around the body anymore ... we cut the main tension and anchor point for the body in half and left all that negative ease there ... and it has no reason to stretch anymore. How stupid are we??

So how do we fix it? Leah Dodrill answered this correctly: we remove the negative ease from the waistline... but not all the negative ... bring the waist back to about 3% instead of 12% and re-curve the waist gradually into the bust and hips again ... we still need some negative ease or the elastic won't work ... But yes, that's how easily you fix this problem. In some cases we may want to remove negative ease at the bust as well (eg; where there's no straps holding the bust in place) but not quite as much as we remove from the waist ... this is something that depends on the design. 

The lesson here is to work out what's causing the problem and resolve that, instead of thinking that spandex is forgiving so you just pull it tighter until it fixes itself.

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