Quick answer: GSM (grams per square meter) measures fabric weight. Lower GSM = lighter, thinner, more sheer; higher GSM = heavier, more opaque, more supportive. For swimwear, leggings and dancewear you generally want a mid-to-heavy weight so the fabric stays opaque under stretch and holds its shape.

What GSM tells you

GSM measures how much a square meter of fabric weighs — the most reliable way to compare stretch fabrics, because density drives opacity, support and durability.

Light vs. heavy weight

Lighter: soft drape, more sheer — good for overlays and linings. Heavier: opaque, supportive, compressive — better for swimwear and leggings where you don’t want sheerness under stretch.

Choosing weight by project

Swimwear & leggings: mid-to-heavy. Dancewear/leotards: mid-weight milliskin. Overlays: lighter mesh. Structured pieces: heavier knits or stretch vinyl.

The opacity test

Stretch a swatch over your hand or a white surface. If it goes sheer under tension, size up in weight — the #1 cause of see-through swimwear and leggings. Order a sample first. See related terms in our glossary.

What does GSM mean for fabric?

GSM is grams per square meter, a measure of fabric weight. Higher GSM means a denser, more opaque and supportive fabric.

What GSM should I choose for leggings or swimwear?

Heavier GSM around 240 plus suits squat-proof leggings and swimwear; lighter weights suit linings and overlays.

Where can I buy spandex in different weights?

Stretch House sells spandex in a range of weights by the yard at stretchhouse.com, with free samples and worldwide shipping from New York since 2004.

Frequently Asked Questions

What does GSM mean in fabric?

GSM stands for grams per square meter, a measure of fabric weight. Higher GSM means a denser, heavier and usually more opaque fabric.

What GSM is best for leggings?

Squat-proof leggings generally use around 220 to 280 GSM for opacity and support, while lighter activewear can use less.

Is higher GSM always better?

No. The right weight depends on the project. Lightweight mesh suits overlays, while heavier knits suit leggings, dancewear and structure.

How does GSM affect opacity?

Heavier, higher-GSM fabric is typically more opaque, while low-GSM fabric can be sheer, especially in light colors when stretched.