I have a California King that is very firm. So much so that I was considering replacing it when a co-worker mentioned toppers. Been sleeping on this for a month and I am pleased to say I sleep MUCH better now. Itza nice! After unpacking, the topper returned to its original shape within a couple of minutes. Didn't notice any unpleasant odor either. Arrived by FedEx around 6:30 p.m. (sure glad I don't have THAT job), and slept on it that night.