Welcome to the new and improved Proflex / K2 Tech Forum!
Just don't do what I did - I used to freeze the cleaned empty bladder to keep mildew at bay and then run under a hot tap when I wanted to refill. One time I thought, oh I'll be clever, I'll microwave the bladder for a few seconds to get rid of the couple of bits of ice in the tube and sac... 10 seconds later I had a melted bladder Sorry doesn't help with your purchase really unless some are microwaveable!!