I have 3 pairs now and they have all been through many washes and are still springy and stretchy so they don't sag. If you are looking for the warmest moisture-wicking material, alpaca is the right choice. They last forever and don't stink, and even if they do after a very long time, just hang them up or throw them over a chair and they smell nice. This is when you can't get to the washing machine. Maybe bacteria in alpacas just can't multiply well. I once found a pair at a fiber fair and loved it. They didn't take the washing well and sagged a bit. But not this one.