Firm in the store. Baggy over the knees three months later.
That legging hasn’t worn through. It’s lost recovery, which is a different failure from a hole or a split seam, and a much harder one to spot on a rail. The fabric still stretches as far as ever. It just doesn’t come back.
People talk about stretch and recovery as one property. They’re two. Stretch is how far fabric extends under load. Recovery is how fully and how fast it returns once the load is off. A fabric can stretch a lot and recover badly: that’s a typical cheap cotton-elastane rib. It can stretch modestly and recover brilliantly: common in a firm technical knit with low elastane. Which one a garment needs depends on its job, and the knee, seat and waistband are where the difference shows.
How elastane wears out#
Elastane, sold as spandex in some markets, supplies most of the recovery in activewear. It’s used at low percentages, commonly about 5 to 20 percent, and that number on the label is worth reading. A synthetic-specific detergent such as Nikwax Tech Wash usually runs $11.50–$30.40 depending on bottle size (10 to 33.8 fl oz), per nikwax.com and REI, Oct 2026.
The fiber’s molecular structure is engineered to unfold and refold. Cycle it enough and it fatigues: it stops returning fully and the garment takes on whatever shape it was held in. Heat speeds that up. So does chlorine. So do oils from sunscreen and some skincare. Knees, seat and the front of the waistband fatigue first because they get cycled most.
More elastane gets you more stretch and a firmer first feel. It doesn’t get you more durability. The more a garment leans on elastane, the more its shape depends on the part that fails earliest.
The knit matters as much as the fiber#
The knit itself is the second source of stretch, which is why fiber content alone can’t tell you whether something will bag out.
Single jersey is a looped structure that stretches easily both ways and recovers through loop geometry as well as elastane. Interlock has two interlocking faces, so it’s thicker, more stable, curls less and recovers well without relying entirely on the stretch fiber. Rib knit has deep vertical wales and stretches far more around the body than along it, which is why it’s used for cuffs and waistbands that need a firm local grip. Power mesh is a dense, high-modulus knit, often used in panels, built for compression rather than softness.
Denser knits with tighter loops usually hold shape better because the loops support each other and the yarn has less room to migrate. A loose, open knit with the same elastane content sags sooner.
Wovens and stretch yarns#
Not all stretch fabric is knitted. Stretch wovens, used in training shorts, trousers and some outer layers, get their give from elastane spread among interlaced yarns rather than loops. They resist abrasion and hold shape firmly, but recover less forgivingly: overload a woven and it stays stretched.
Some stretch comes from the yarn itself, as bicomponent or textured yarns that coil and uncoil. These handle heat and chlorine better than elastane but stretch less, which suits light support rather than compression.
What kills recovery#
All well established, mostly avoidable:
- Hot tumble drying. The most direct cause of bagginess, since heat sets the relaxed fiber in whatever configuration it’s in.
- Chlorinated pools. Chlorine degrades elastane chemically, so pool swimwear dies sooner than the same fabric used in fresh water.
- Hot washes. Warm is usually enough for one session’s wear, and cool is kinder.
- Sunscreen and body oils. They act on the fiber and build up in the fabric.
- Fabric softener. Coats the fiber and does nothing for recovery.
- Storing damp. It doesn’t directly destroy elastane, but it drives the bacterial growth that damages fabric and sets odor.
Cool wash, mild detergent, no softener, flat dry or low heat. That covers most of the risk.
Test it before you buy#
You can’t feel recovery by touch, so this one-minute fitting-room test is the most useful one you’ve got.
Grab the fabric at the thigh or upper arm between both hands, stretch firmly across the width, and hold a few seconds. Release and watch. A prompt return to the original width means it’s working. Staying expanded, or creeping back over several seconds, means weak recovery already: usually high elastane relative to knit stability, or fabric that’s already aged.
Then test what matters most: waistband, cuff, strap. Pull the waistband sideways and let go. Snap back or stay flared? A band that stays flared on a new garment will only get worse.
If you can, look at a used or returned piece too, since worn fabric shows the failure honestly. Leggings baggy at the knee on the rail will be baggier in a month.
Buy the least elastane that does the job#
Pair it with the densest knit available in that style. A firm interlock with around 10 percent elastane will usually outlast a very stretchy fine jersey with 20 percent, and it’ll feel firmer, not softer. Lululemon’s Align High-Rise Pant 25” is a useful reference: its Nulu fabric is 81% nylon and 19% Lycra elastane, and it usually runs $69–$98 depending on sales, per lululemon.com and Fleet Feet, Oct 2026.
Two more rail checks. Look at seams at high-stress points: a seam stretched past its thread’s capacity puckers. And check whether the elastane runs both directions or only one, often visible as a rib direction or a two-way stretch claim on the label.
Care does the rest: cool wash, no softener, no hot dryer, no chlorine, and the elastane works for its full life. Once recovery goes, seam integrity and the wicking finish usually follow within a few months. At that point it belongs in the donation bin or the rag pile.