From the manufacturer:
"The biggest difference between our fabrics and 99% of them out there is our technology is yarn based – that means we build the properties into the construction of the thread (yarn). Most everyone else uses chemicals to produce the desired function and every time you wash it – the attribute gets dissolved down the drain and finally you're left with a product that does not do anything."
ColdSacs - 75% micro polyester, 25% Jade micro nylon – 2 way stretch
WarmSacs - 88% micro polyester, 12% spandex – 4 way stretch