I'm looking for some foam that can be used as an airtight seal, but it needs to be soft. Maybe a little bit firmer than memory foam, if you know how soft that is. So it needs to be closed cell foam, that's relatively soft, but I don't know what kind of foam to search for. I'd have to buy it online because I don't know of any stores that specialize in foam. I just don't know what kind of foam to look for. I don't know any of the names. Anyone have any suggestions?