Polyurethane foams are produced by reacting polyols and diisocyanates, both products often derived from crude oil.

The main diisocynate used in the production of flexible polyurethane foam is TDI (Toluene diisocyanate). Some foams, notably so-called visco-elastic or memory foams, can also be made with MDI (Methylene diphenyl diisocyanate). Moulded foams are more often made with MDI. 

When mixed with polyols, which are long alcoxyether chains, these chemicals form the building blocks of polyurethane.

Depending on the specifications of the foam to be produced, other substances are mixed with the diisocyanates and the polyols: additives, catalysts, colorants, water/carbon dioxide. 

In some instances – notably when required by local legislation – flame retardants are added to formulations to increase the fire resistance of polyurethane foam. It should be noted that spontaneous ignition is not possible for flexible foams under normal operating temperature.