Elastic Performance

I'm often asked if elastic choice can affect a pattern. My answer is always a very simple yes. Strangely I'm never asked why. It seems we all know how elastic type and tension can affect a garment, but not how much or why.

Swimwear is manufactured almost exclusively with vulcanized flat rubber ribbon elastic. These come in varying thicknesses and widths. Generally, the thicker and wider the elastic, the more rebound tension it offers. Flat rubber also has a gentle increase in rebound tension as it's stretched out, rather than the sudden onset of rebound you find with woven and knitted elastics. A problem all elastics have is that they deteriorate rather quickly when exposed to chemicals, heat or UV.

Which elastic is appropriate depends on its application. A simple fold over elastic in a swimsuit leg line, for example, is usually 8-11mm wide and around 0.6mm thick. If you were to choose narrower elastic it would not only lack the strength to stabilise the garment, but it would also dig into a soft part of the body while trying. Besides being uncomfortable, this would look awful.

Elastic wider than 13mm requires a great deal more force to stretch it and as such it doesn't have a wide working range on the body. This makes it unsuitable for areas like the leg line (which change dimension significantly during movement) but very useful in bust support panels like shelf bras.

Wide flat elastics also have a problem going around small radius curves and cut outs. You'll know your elastic is too wide for a small radius if the elastic rolls out rather than sits flat. What is happening is the outside edge of the elastic is stretching beyond its workable limit while the inside edge is unstretched. Because you can't practically change elastic widths mid seam, you need to be aware of what minimum radius each elastic can tolerate.

Bound edges and straps typically utilize slightly smaller elastic about 5-7mm wide and 0.5mm thick. They can tolerate being thinner and narrower because they are essentially wrapped in an elastane fabric which increases the overall rebound tension of the binding or strap. Bound elastic while very stable, does not have the softness or stretch range of fold over elastic seams.

So now we've decided which elastic to use, how 'tight' do we need to make it? Well this goes back to the amount of negative ease already added to the garment. If you employ 12% negative ease and 3% elastic tension then the elastic is effectively stretched 15% on the body. If you were to use only 5% negative ease for dancewear, clearly you'd need to increase your elasticator tension significantly to attain the same final tension on the body.

Tip While dancewear clients are used to seeing garments looking 'gathered' because of the extra elastic tension, retail swimwear would be completely unacceptable on the sales shelf if it looked gathered. Swimwear on the sales shelf needs to sit relatively flat, forcing a very difficult balancing act between negative ease, elastic tension and comfortable fit.