Maybe you are right about the heat in an attic deteriorating them plus when used in braids and ponytails aren't they twisted and doubled up multiple times which may lead to shorter life. I am just guessing or hoping this is the case. Those 2mm ones was the size I have been looking at hoping that they would fit perfectly in one loop without having to twist and double up. I thought by them lying flat without the twist and doubling up they would be more advisable. Thanks for the help. 