Depends what you are trying to do. Size, roll internal, etc. I try to roll all of our preps at room temperature (ie 72.*) Sometimes I need to speed the process up some and a little more heat will help. Never more than 100* for prepping. I try to size them with as low of heat as I can get away with -- most times 100* is sufficient....rarely do I have to go higher than that, but there's always that occasion where I'm trying to stretch or shrink something an unreasonable amount but try to do it anyway.