Most of my dies and mats are stored flat in a drawer. I have the die rack but have too many dies to use racks for them all. I bought the Go as soon as it was available to buy and all of the dies that were available then. They have been stored flat since I bought them and I haven't noticed any problem. I have noticed the first dies seem to have better foam on them then the newer dies and the first dies seem to be sturdier then the newer ones.