Originally Posted by cyccommute

Lycra doesn’t have elastic in it, it is the elastic. More precisely, it is an elastomer which is a polymer that stretches. Rubber is also an elastomer but rubber’s molecular structure is very different and much more susceptible to degradation through a large variety of means. It is repeating chains of isoprene. The structure can be broken because of exposure to heat and/or light. It’s susceptible to oxidation, especially ozone oxidation. All these ways of degrading the polymer involve cleaving the isoprene molecule. Cleave enough of them and the rubber becomes less stretchy.

Lycra, on the other hand, has a structure that contains both very rigid molecular structures and molecular structures that act a bit like springs. The rigid structures give the lycra strength and the springy structures give it the stretch. Neither structure is particularly susceptible to degradation. The stretchy bits relax after being stretched but they don’t really relax completely. They lose stretch over time. Heat rearranges the structure and recoils the stretch. Hang drying doesn’t accomplish the same thing.

Yes, I’ve had some shorts that eventually broke some of the spandex fibers but it took several years for that to happen. I got a lot of value out of those shorts before they wore out.