Fabric Weight (GSM) Explained: What to Choose for Swimwear, Leggings and Leotards
GSM tells you how heavy a fabric is, and it changes everything from opacity to compression. A practical guide to choosing the right weight for each garment.
GSM, or grams per square meter, is the most useful single number on a fabric spec sheet. It tells you how heavy a fabric is, and weight affects opacity, compression, drape, durability and even the price of your finished garment. Here is how to read it and what to choose.
What GSM means
GSM is the weight of one square meter of fabric in grams. A 210 GSM tricot weighs 210 grams per square meter. The higher the number, the heavier and usually thicker the fabric. Because it is measured per area, GSM lets you compare fabrics fairly regardless of roll width.
Some US suppliers also list ounces per square yard. To convert, divide GSM by about 33.9: a 240 GSM fabric is roughly 7 oz per square yard.
Why weight matters
- Opacity: heavier knits are less see-through, especially when stretched. This is critical for leggings and light colors.
- Compression and support: heavier, higher-spandex fabrics hold the body more firmly.
- Drape and comfort: lighter fabrics move freely and feel cooler; heavier fabrics feel more structured.
- Yield and cost: fabric is sold by the yard, but heavier fabric uses more fiber, so price per yard usually rises with weight.
Typical weight ranges by garment
These are common starting points, not strict rules. Construction, fiber and spandex content matter too.
| Garment | Typical GSM | Notes |
|---|---|---|
| Swim and activewear lining | 90–140 | Light, smooth, adds opacity without bulk |
| Swimwear (bikinis, one-pieces) | 180–230 | Balance of stretch, coverage and quick drying |
| Leotards and dancewear | 200–240 | Needs strong recovery; foils and holograms sit here too |
| Everyday leggings and tops | 220–260 | Comfortable with good coverage |
| Squat-proof and compression leggings | 260–320 | Higher spandex and denser knit for support |
| Loungewear, fleece and terry | 280–400 | Soft, warm and structured |
Examples from our range
- Helenca Lining: 100% nylon, about 100 GSM, a classic swim lining.
- Sportivo: 82% nylon, 18% spandex, 210 GSM matte tricot for swimwear and dance.
- Super Fino: 82% nylon, 18% spandex, 230 GSM, a little more coverage for swim and activewear.
- Power Jersey: 78% nylon, 22% spandex, 290 GSM for compression and shapewear.
GSM is not the whole story
Two fabrics with the same GSM can perform very differently. Also check:
- Spandex percentage: 15–25% gives a firmer, more supportive hold than 8–10%.
- Knit construction: tricot, interlock, jersey and power net each stretch and recover differently.
- Stretch direction: 4-way stretch moves both lengthwise and crosswise; 2-way stretches in one direction.
How to test weight in practice
Order a 1-yard sample, stretch it over your hand or knee to check how sheer it becomes, and sew a quick test piece. Wash it a few times and check recovery. Every Rex fabric page lists GSM, width and stretch, and we can share a technical data sheet on request.
FAQ
What is a good GSM for leggings?
Around 220–260 GSM for everyday leggings, and 260–320 GSM with higher spandex for squat-proof or compression styles.
What GSM is best for swimwear?
Most swimwear uses 180–230 GSM tricot, often with a 90–140 GSM lining for coverage.
Is higher GSM always better quality?
No. Higher GSM means heavier, not better. The right weight depends on the garment: a heavy fabric makes a poor swim lining, and a light one makes poor compression leggings.
Fabrics in this article
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