What is swimsuit fabric?
Swimsuit fabric, also called swim knit or swimwear fabric, is a stretch knit designed to handle water, sun, and repeated stretching. Most are blends of nylon or polyester with spandex (elastane or Lycra). The knit is typically smooth and tightly constructed, with stretch in both directions, and sold by the yard in solids and prints.
Because spandex is the stretch ingredient, much of what you know about handling it carries over. Our guide to sewing spandex covers needles, thread, and stitches in more depth.
Nylon spandex versus polyester spandex
The two most common swim fabrics are:
- Nylon/spandex: Often soft and silky, with good stretch and recovery. Many sellers describe it as the more luxurious feel, and it is common for fitted swimsuits and bikinis.
- Polyester/spandex: Generally firmer, holds color well, and is often noted for chlorine resistance. It is commonly used for competitive and heavy-use swimwear and for activewear.
Both can work well. Exact performance depends on the manufacturer, the proportion of spandex, and the knit, so read the product description and, if possible, order a swatch. Some fabrics are made from recycled fibers, which is worth looking for if that matters to you.
Stretch, recovery, and lining
- Four-way stretch: Swimsuit patterns normally assume a fabric that stretches both across and along. Check your pattern for the stretch percentage it is designed for and test your fabric against the pattern’s stretch gauge.
- Lining: Swimsuits are normally lined. Swim lining is a lightweight stretch knit made for the purpose and is sold in nude, white, and black among other colors. The lining affects fit, so choose one with stretch similar to the outer fabric. If the lining is much less stretchy, the outer fabric can end up baggy.
- Opacity: A tight knit is less likely to turn see-through when wet, but light colors can still show through, so lining the front and crotch is a common precaution.
How many yards of fabric do you need?
The amount varies with the style, the size, and the width of the fabric (swim knits are often around 58 to 60 inches wide, though this varies). Bikinis use much less fabric than one-pieces, and a lining requires additional yardage. The most reliable source is the yardage chart on your pattern, which lists amounts by size and view. Buy a little extra for test stitching and for matching prints.
Needle, thread, and elastic
- Needle: A stretch or ballpoint needle helps avoid skipped stitches and snags. Changing to a fresh needle at the start of the project is a common tip.
- Thread: Polyester thread is the standard recommendation, since cotton may not hold up well to salt water and chlorine.
- Elastic: Choose elastic sold for swimwear. Some sellers recommend rubber-based or cotton-covered elastic that resists chlorine, and widths around 3/8 inch for leg and neckline openings are common. Fold-over elastic is another option for finishing edges. Check the product description for chlorine resistance.
Cutting and preparation
- Cut a single layer, using a rotary cutter and weights on a cutting mat, because slippery knits shift when layered.
- Follow the grainline arrows and the direction of greatest stretch indicated on your pattern, which is usually around the body.
- Cut the lining to match the outer pieces.
- Test your stitch settings and your elastic tension on scraps of the actual fabric and lining before you start.
Sewing techniques
- Stitches: Use a narrow zigzag, a three-step zigzag, or a stretch stitch on a regular machine, or an overlock stitch on a serger. A straight stitch can pop when the fabric stretches.
- Seam allowances: Many swimwear patterns use narrow seam allowances. Follow your pattern.
- Construction order: Patterns differ, but a common method makes the outer swimsuit and the lining separately, then bastes the two together at the edges before applying elastic. This is also a good time to try the swimsuit on to check the fit.
- Elastic length: Some designers cut elastic shorter than the opening, with a rule of thumb of roughly three-quarters of the opening length. Your pattern will usually give exact lengths, so follow those. Mark both the elastic and the edge into quarters and match the marks as you sew.
- Attaching elastic: Stretch only the elastic to fit, not the fabric, while sewing, then fold it over and topstitch.
- Topstitching: A zigzag stitch, a twin needle, or a coverstitch machine gives a finish that still stretches.
Is sewing swimwear difficult?
Swimwear has fewer pieces than many garments, which is a big part of why many sewists find it approachable. The challenge is working with a slippery, stretchy fabric and getting elastic tension right. Start with a simple pattern, such as a basic one-piece or bikini bottom, and make a test version from inexpensive stretch knit first. Patterns that are labeled for beginners often include helpful tips on elastic placement.
Caring for swimwear
Rinse your swimsuit in cool, fresh water after wearing it, wash it gently by hand or on a delicate cycle, and let it air dry away from direct heat. Fabric softener and high heat can shorten the life of the elastic fibers. Follow any care instructions given by your fabric seller.
What fabric should I use for a swimsuit?
A four-way stretch nylon/spandex or polyester/spandex swim knit designed for swimwear, paired with a swim lining and swim-grade elastic, is the common choice. Ordinary jersey or other knits not designed for swimming may sag, fade, or lose stretch when wet.
Related fabrics
Swim fabric is only one of many specialty materials. For more on stretch knits, read about sewing spandex. If you are curious about lightweight, see-through cloth for cover-ups, our guide to sheer fabric types is a good place to begin.