A chemical process during manufacture that increases the durability of closed cell foam. Polyethylene foam is made up of millions of carbon molecules tied end to end. The molecules form a chain that may be 400,000 molecules long. When heat is applied in foaming, the cross linking agent reacts and chemically ties the chains together in a strong, cross-linked carbon bond creating a solid unified mass. Testing has repeatedly proven that cross-linked polyethylene substantially outlasts non cross-linked by as much as 7 times! The cell structure will not break down under repeated bending or compression, even when exposed to a wide range of temperatures or environmental conditions. And so, while other foams may look and feel virtually identical to cross-linked, they are unable to provide excellent shock absorption and cushioning, resiliency and fatigue resistance.