Quick Answer: The mirror squat test under fitting room lighting misses most opacity failures. Fabric goes sheer where it stretches most, which on curvier bodies is the upper back thigh and the outer hip — places a mirror squat does not load. Test in bright daylight, in a deep bent-over position, and check the seams specifically, since seam allowances are where thinning shows first.

Everybody knows to squat in the fitting room. Almost nobody knows that the squat is testing the wrong part of the garment.

A squat loads the back of the thigh and the seat, which is genuinely where a lot of leggings fail — but on a curvier frame, the highest-stretch zone is often somewhere else entirely, and fitting room lighting is designed to be flattering, which in this context means it hides exactly what you are trying to see.

Why does the standard squat test miss things?

Three reasons, and they compound.

Lighting. Fitting rooms use warm, diffuse, downward light. Sheerness shows up under bright directional light from behind, which is the opposite. A pair of leggings that look solid in a store can be visibly transparent on a sunlit sidewalk with the sun at your back.

Stretch percentage. A squat stretches fabric across the seat by roughly 30 to 40 percent for most bodies. A deep forward fold or a hip-width lunge can push the outer thigh past 50 percent. Fabric opacity does not degrade linearly — it holds, holds, holds, and then goes sheer past a threshold. Testing at 35 percent tells you nothing about what happens at 55.

Where the stretch actually lands. This is the part specific to curvier bodies. If your hip-to-waist difference is large, the fabric across the outer hip and upper back thigh is under more baseline tension than it is on a straighter frame, before you move at all. That means less stretch reserve remains when you do move. The failure point migrates from where the brand tested it to somewhere else on your body.

What does a proper opacity check look like?

Five checks, in order of how much they tell you.

1. Daylight, from behind. Stand with your back to a window and have someone photograph you, or use your phone’s rear camera and a mirror. This is the single most informative test and it takes fifteen seconds. Backlighting reveals what front lighting hides.

2. Deep forward fold. Not a squat — a full bend at the hips with straight legs, which puts maximum stretch across the back thigh and seat simultaneously. If they hold here, they hold anywhere.

3. Wide stance. Feet wider than hips, slight knee bend. This loads the inner and outer thigh laterally, a direction squats do not test.

4. Seam check. Look specifically along the inseam and the back rise seam. Seam allowances are folded fabric under tension, and thinning shows there before it shows in flat panels. If the seam looks lighter in colour than the fabric beside it, the fabric is being pulled thin.

5. The stretch-and-hold. Grab a section of fabric between two hands and stretch it, then hold it up to a light. This tells you the true opacity ceiling of the fabric regardless of your body. Do this on the thigh panel, not the waistband.

Which fabric specs actually predict opacity?

Two numbers on the label are worth learning to read.

Fabric weight, usually given in GSM (grams per square metre) when brands publish it. Under about 200 GSM, opacity under high stretch is a gamble. 220 to 280 GSM is the range where most reliably opaque leggings live. Above 300 GSM you are into compression territory — very opaque, warmer, and heavier than many people want in late summer.

Spandex percentage. Counterintuitively, higher spandex content does not mean better opacity. It means more stretch, which means more thinning at the same load. A legging with 12 to 20 percent elastane in a heavier knit usually outperforms one with 25 percent in a lighter knit.

The colour caveat that catches people out: light colours and heathered greys are structurally worse, and the same fabric will read as sheerer in grey than in black. If you love a style and it is available in both, buying black is not a compromise — it is buying the version that will still look good in eighteen months.

One more: doubled front panels. Some brands double the fabric across the front rise, which solves the most visible failure zone cheaply. Worth checking by feel when you try them on.

Myth vs Fact: legging opacity

Myth: Expensive leggings are always opaque. Fact: Price correlates loosely with fabric weight and not at all with how a fabric behaves on your specific proportions. Plenty of premium leggings are cut for a straighter frame and go sheer on a curvier one at the outer hip.

Myth: If they are opaque when new, they stay opaque. Fact: Opacity degrades with washing and with the fabric relaxing over months of wear. The realistic expectation for a mid-weight legging worn twice a week is 12 to 18 months before noticeable thinning. Hot water and machine drying compress that timeline sharply.

Myth: Sizing up fixes sheerness. Fact: Sometimes, but often not. Sizing up reduces stretch tension, which does help — but it also means excess fabric bunching elsewhere, and if the sheerness is a fabric weight problem rather than a fit problem, a bigger size in the same fabric fails the same way.

Myth: You can tell by rubbing the fabric between your fingers. Fact: Hand feel tells you about softness, not opacity. Thin buttery fabrics feel wonderful and are frequently the sheerest ones on the rack. Hold it to the light instead.

FAQ: Legging Opacity Questions, Answered

Are compression leggings always more opaque?

Usually yes, because compression fabrics are heavier and denser by design. The trade-off is heat retention and a firmer feel that not everyone wants for everyday wear.

Why do my leggings look fine in the gym mirror and sheer in photos?

Gym mirrors are usually lit from above and in front. A phone camera with a window behind you is backlighting, which is the harsher and more accurate test. Trust the photo.

Do black leggings ever go sheer?

Yes, particularly after fading. Black that has drifted towards charcoal has lost dye density, and dye density contributes to perceived opacity. Wash inside out in cold water to slow this down.

Is there a way to fix leggings that are slightly sheer?

Not really, but you can work around it — a longer top, or wearing them as a base layer under shorts. If they are sheer enough to bother you now, they will get worse, so it is usually better to relegate them to home workouts than to keep trying to make them work in public.

TL;DR:

• Test in daylight with the light behind you, not in fitting room lighting.
• Use a deep forward fold and a wide stance, not just a squat — the failure zones on curvier bodies are the outer hip and upper back thigh.
• Look for 220 to 280 GSM and moderate elastane; higher stretch percentages often mean worse opacity.
• Check the seams — thinning shows there first.

The reason this test matters is that opacity is one of the few legging qualities you cannot fix later and cannot judge by feel. Five extra seconds of holding the fabric up to a window at the point of purchase saves a garment you will otherwise never quite trust.

See It in Motion

Seen here: Super High Waist Embossed Yoga Leggings with Inner Pocket — shop it on bubblelime.com