My husband and I looked at many different memory foam mattress toppers. We were looking for one that was just memory foam, and not a combination. This four inch one seemed to be just the ticket! We took it out immediately after it arrived, and it expanded very quickly and had no odor that we could smell. We put it on the bed a few hours later because we didn't really have anywhere to let it rest without our pets getting to it. It hugs you when you lay on it, its extremely comfortable, just what we were looking for to make our old california king a bit more comfortable. It definitely renewed our mattress.