(Continued from Part 1) The three major kinds of foam used in mattresses are polyurethane foam, visco-elastic memory foam, and latex foam. Each kind of foam has variations. First, there are different ingredients in these foams. Then there are different densities and firmness levels. Now gel is infused into different foams to add desired characteristics. Polyurethane Foam Polyurethane (PU) foam is made by linking large molecules, usually isocyanates, to each other with modified oil...