You bend into a squat, catch yourself in the gym mirror, and your leggings have gone transparent. It's a common enough experience that "squat proof" has become a product category.
The good news is that it's predictable. Here's what actually causes it.
Cause one: the fabric is too thin
The most obvious reason. Fabric weight is measured in GSM — grams per square metre. Below roughly 200 GSM, most knits will show skin when stretched over a curved surface.
Thin fabric feels light and cool on the hanger, which is why it sells. It just doesn't survive a deep squat.
Cause two: not enough elastane
Elastane, spandex and Lycra are the same thing under different names. It's what lets fabric stretch and — more importantly — recover.
Below about 15% elastane, fabric stretches but doesn't spring back well. Once it's stretched thin across your seat, it stays that way and the weave opens up. Our high-waisted yoga leggings use an 80/20 nylon-spandex blend for exactly this reason.
Cause three: the wrong size
Leggings a size too small are stretched near their limit before you even move. Any additional stretch from squatting pushes the weave past the point where it's opaque.
Counter-intuitively, leggings that are too large can also go sheer, because loose fabric bunches and thins unevenly rather than distributing tension.
Cause four: light colours
The same fabric in black and in light grey will not perform the same. Light colours show shadow and skin tone through the weave far more readily.
If you're unsure about a fabric, buy it in black first.
Cause five: age
Elastane degrades. Every hot wash, every tumble dry, every hour in direct sun shortens its life. A pair that was opaque a year ago genuinely may not be now.
Washing cold and air drying slows this considerably — see our activewear care guide.
The squat test
Do this before you wear new leggings out:
- Put them on and stand in front of a mirror in good light.
- Squat down as low as you comfortably go.
- Look at the seat and the back of the thighs — the areas under most tension.
- Ask someone, or use your phone camera, since you can't see the back yourself.
If you can see skin tone or the outline of underwear, they aren't squat proof. Better to find out at home.
What to look for when buying
- Elastane content of 15% or higher — check the composition, not the marketing
- Thicker fabric — if the listing gives a GSM, look for 200 or above
- Interlock or double-knit construction rather than single jersey
- A gusset in the crotch — a diamond-shaped panel that reduces seam stress and improves fit
- Flat or bonded seams rather than thin overlocked ones
What about bike shorts?
The same rules apply, but shorts are under less tension across a smaller area, so they tend to be more forgiving. Our high-waisted biker shorts use a 75/25 nylon-spandex blend.
If you're deciding between the two, we compared them in bike shorts vs leggings.
The short answer
Buy thicker fabric with at least 15% elastane, in your correct size, and wash it cold. That covers almost every case.
Shop women's bottoms at WTD.