Are Your Leggings Squat-Proof? Here Is How to Test Them

By the Sale Splash Online team · Updated October 16, 2026

To test if leggings are squat-proof, put them on and stand with your back to a mirror in bright daylight. Then do a deep squat and bend forward from the hips. If you can see skin, underwear or a lighter patch where the fabric stretches, they are not squat-proof. A squat-proof pair shows no colour change at full stretch.

Squat-proof means the fabric stays opaque when stretched. Plenty of leggings look perfectly solid on the hanger and turn sheer the moment you bend forward. Here is how to check before you find out the hard way in a gym class.

The test, in thirty seconds

1. Put the leggings on.
2. Stand with your back to a mirror, or set your phone camera up behind you.
3. Do a deep squat and hold it, then bend forward from the hips.
4. Look at the seat and the backs of the thighs. If you can see skin tone or underwear outlines, or the fabric visibly lightens where it stretches, they are not squat-proof.

Do this in bright light, ideally daylight. Gym lighting is unforgiving in a way your bedroom is not.

This is the same test the industry falls back on. When Lululemon’s sheer pants were on the news in 2013, then-CEO Christine Day told analysts: “The only way that you can actually test for the issue is to put the pants on and bend over” (reported by the Wall Street Journal, via NBC Los Angeles, March 2013).

What makes fabric go sheer

Knitted fabric is a mesh of yarn loops. Stretch it and the gaps between loops open up. Datacolor, a maker of colour-measurement instruments, notes that “stretching increases the space between yarns and can make the background more visible”. That is why it recommends measuring stretch fabrics at realistic extension (Datacolor). Lab research backs this up. A 2023 study of weft-knitted fabrics for seamless garments found that light transmission increases with tensile strain, and that biaxial stretching (both directions at once) lets the most light through (Zhang, Ge & Liu, Textile Research Journal, 2023). A deep squat stretches the seat both ways.

The size is too small

This has the same root cause as rolling waistbands. Fabric stretched beyond its intended range thins out and lets light through. A pair that is sheer in a Medium is often completely opaque in a Large. Before writing off a style, try the next size up.

The fabric is too thin

Weight is the single biggest factor. Stretch House, a spandex fabric supplier, says squat-proof leggings generally use around 220 to 280 GSM. It also notes that heavier, higher-GSM fabric is typically more opaque, while low-GSM fabric can be sheer (Stretch House). If a legging feels papery between your fingers, it will be sheer under stretch. Textile researchers describe the same idea as “cover factor”: how fully the yarn covers the fabric area determines how much light passes through (Szmyt & Mikołajczyk, Autex Research Journal).

The colour

Light colours, greys and pastels show sheerness far more readily than black. Grey is notoriously the worst, because it shows both sheerness and sweat marks. If you are buying a pale colour, the fabric needs to be correspondingly heavier.

Cut-and-sew versus seamless

Seamless knit leggings are made as a tube on a circular knitting machine with no side seams, so there is no seam to gape under tension. They tend to hold opacity better through the seat than cheaper cut-and-sew construction. The same 2023 study found that plating a coarser elastic yarn into a seamless knit tightens the loops and reduces light transmission.

What affects squat-proofing

The Lululemon recall: why testing matters

In March 2013 Lululemon found that some black Luon bottoms were too sheer. The fabric’s makeup had not changed, but in the company’s words, “the coverage does not”. The affected shipments represented approximately 17% of all women’s bottoms in its stores, and were pulled on the weekend of March 16, 2013 (Lululemon FAQ via ABC13, March 2013). The company estimated lost revenue of $57 million to $67 million for the year. Day said black Luon was “a very technical and sensitive product to manufacture” (Lululemon press release, March 21, 2013). If a premium brand’s own fabric can slip past quality control, a thirty-second check at home is worth doing on every new pair.

Quick buying rules

• Buying for squats, deadlifts or yoga? Choose black or a dark colour in a heavier knit
• Buying pale colours? Treat them as casual or low-impact wear unless you have tested them
• Between sizes? Size up. It helps opacity as much as it helps comfort

If a pair does not pass the test, our returns policy covers you within 14 days of delivery.

Frequently asked questions

What does squat-proof mean?

Squat-proof means a legging stays fully opaque when the fabric is at full stretch, such as in a deep squat or forward bend. No skin, underwear or lightening of colour shows through at the seat or thighs.

How do you test if leggings are see-through?

Wear them with your back to a mirror (or a phone camera behind you) in daylight. Do a deep squat, hold it, then bend forward from the hips. Any visible skin, underwear outline or lighter patch means they are not squat-proof.

What GSM should squat-proof leggings be?

A spandex fabric supplier puts squat-proof leggings at around 220 to 280 GSM. Heavier fabric is generally more opaque. Colour and fit matter too, so a pale or too-small pair can still go sheer.

Why are my leggings see-through when I squat?

Stretching opens the gaps between the knitted loops and lets more light through. The usual causes are leggings that are a size too small, fabric that is too lightweight, a pale colour, or an old pair whose elastane no longer recovers.

Does sizing up make leggings less see-through?

Often, yes. A larger size stretches less over the same body, so the knit stays denser. A pair that is sheer in a Medium is frequently opaque in a Large.

Are seamless leggings more squat-proof?

They tend to be. Seamless leggings are knitted as a tube with no seam to gape under tension, and denser seamless knits block more light. Thin seamless styles can still go sheer, so test them too.

Shop this guide: gym leggings · seamless leggings · scrunch-back leggings