There are many types of diisocyanates the foremost of which are: methylene diphenyl diisocyanate (MDI) and Toluene diisocyanate (TDI) are aromatic diisocyanates, while hexamethylene diisocyanate (HDI), methylene dicyclohexyl diisocyanate or hydrogenated MDI (HMDI) and isophorone diisocyanate (IPDI) are aliphatic diisocyanates. Along with polyols, which are long alcoxyether chains, these chemicals form the building blocks of polyurethane.

Effectively polyurethane (PU) is a plastic material (a polymer) that is derived from the chemical reaction between diisocyanates and polyols; when mixed together, they polimerise. Polyurethanes would not exist without diisocyanates and polyols.