How leggings lose their shape at the knee

Short answer: The knee bends thousands of times a day, and the fabric is stretched each time. Held stretched for hours, the elastane cannot draw back, and a bag forms. The bag is not in itself a sign that anything is wrong.

The bending is constant

With every step, every staircase and every time you sit down, the fabric over the knee is stretched. No other part of a legging works harder. The fabric has to follow the knee back and forth all day, which is a greater strain than the rest of the leg puts on it, even if it is not easy to see.

Time without rest is the problem

If you sit for a long time with a bent knee, the fabric is held stretched without coming back. The elastane adapts to the new shape, and that is the shape you see when you stand up. It is not a matter of weak fabric, but of fabric that has had no time to draw back. See bamboo leggings for women.

Why the bag often disappears in the wash

Water and heat let the molecule chains find their way back. If the elastane is not broken down, the garment looks normal again after a wash. That is a good sign: the bag was a temporary adaptation and not lasting damage. Wash at a gentle temperature so the elastane is not strained more than necessary.

When the bag does not come back

If the bag does not come back after washing, the elastane is used up. The knee then stays bagged out even when you have not been sitting. It happens after long use, at the point where the garment has spent its spring and can no longer restore its shape. See bamboo loungewear for men.

Is it poor quality

Not in itself. All knitted trousers bag after a day of wear, because knit gives over the knee. The difference between a good and a poor garment lies in whether the bag disappears again after a wash or rest. So look at how the garment behaves over time, not only after a single day. See bamboo shorts for men.

Does airing help

Hanging the garment to air helps a little, but a wash works better. Air gives the fabric time to draw back somewhat, but it is water and heat that let the molecule chains find their way fully back. If there is no time to wash, airing is still better than putting the garment straight back on.

Rotate between several pieces

If you wear the same piece day after day, the bag becomes a habit and the elastane never rests. Rotate between several pairs so each gets time to recover. It makes a difference to how quickly the knee goes slack and how long the garment keeps its shape.

Washing and fit

Wash at a low temperature and skip the tumble dryer, because heat is hard on elastane. Choose a size that fits close without pulling, so the fabric is not already stretched before the knee even bends. Fit helps decide how hard the knee has to work in daily life.

Frequently asked questions

When does the bag not come back

When the elastane is used up. The knee then stays bagged out even after a wash, and the garment has spent its spring.

Does hanging the garment to air help

A little, but a wash works better. Water and heat let the molecule chains find their way back, so wash at a gentle temperature and let the garment dry fully.