Chemical Sructure of Polyurethane Foam

Polyurethane is formed when the reaction between Isocyanate and Polyol occur with assistance of blowing agent.

The hardness of Polyurethane is depend on the amount of blowing agent. The common use blowing agent is CFC but had been banned in 1989.

The hardness of the foam also depending on the number of repeating units of soft part and rigid part. As you  can see rigid part is formed from benzene ring carbonyl and nitrogen. meanwhile the soft part is formed from repeating units of carbonyl.

The famous polyurethane used in isocyanate are MDI and TDI

MDI

TDI