Polyurethane foams are made from a reaction of isocyanates (derived from petroleum sources - primarily benzene) with polyols (long-chain alcohols derived from vegetable sources) along with catalysts and other process additives.
Another key ingredient of polyurethane foam is the "Blowing Agent." The blowing agent could be a very-low boiling-point solvent such as HFC-245fa, pentane, methylene chloride, or Carbon Dioxide (created as a by-product of the chemical reaction between isocyanate and polyol making foam).
The final, cured properties of polyurethane foam are directly related to:
A wide variation is possible within all of these constraints.
Each of these attributes will influence the performance of particular polyurethane foam in a specific application, but the most significant attribute influencing the performance of rigid polyurethane foam in almost any application is density (however you measure it, in terms of mass per unit volume of material).
Polyurethane foam can be divided into two categories, closed cell and open cell foam. The closed cell foams are plastics where each bubble that creates the foam is continuous and completely spherical or oblong. Open cell foams are plastics where the cell walls are incomplete and contain holes through which liquid and air can easily travel.