I bought this mattress because I needed a large quantity of foam to redo the cushions on my old wooden-frame couch for a reasonable price. If my intent was to sleep on it and never see the inside it wouldve gotten 5*. As I was buying it specifically to hack up for the foam, I was a bit disappointed. I found once it was unboxed and stripped of tarpaulin bag, plastic wrap, zip cover (which was really nice and will be repurposed in my upholstery project) and stretchy inner cover and got to the guts of the mattress it was not the 4.5" HD foam with 1.5" memory foam on the top as advertised. It is three pieces of lightly bonded foam, which appears to be 4" of HD foam, then 1" of soft foam in the same color as the HD foam, and 1" of very soft blue foam that doesnt really act like memory foam. It'll still work for my couch, but I was disappointed in the construction as I now have 3 layers of foam I need to deal with instead of two.
The smell is minimal and I barely noticed it until I started working with the actual foam.