Polyfoam, also known as polyethylene (PE) foam.
From the manufacturer:
Polycell's range of closed cell non-crosslinked PE Foam products are produced using low density Polyethylene resins with HCFC & CFC free gasses. Along with being a lightweight material, PE Foam is also non-abrasive, chemically inert, water resistant and environmentally 100% recyclable.
PE Foam's soft texture makes it the ideal packaging solution for highly polished surfaces as well as providing cushioning against shock for fragile items.