Poly is short for polyurethane. When people refer to poly foam they are generally referring to polyurethane foam. This is the type of foam used as the material for memory foam. Memory foam is polyurethane foam containing bubbles and certain chemicals that make the foam viscoelastic, meaning that it reverts to its original structure after being compressed. The term ‘poly foam’ is given to standard polyurethane foam not treated in this way. It is simply a foam that can be compressed and used as a support or intermediate comfort foam.