: Polyisocyanurate formulations, and polyurethane formulas. There are distinct differences between the two, both in the manner in which they are produced, and in the performance... of the results. Polyisocyanurate foams (or trimer foams ) are generally low density, insulation-grade foams, usually made in large blocks via a continuous extrusion process. These blocks... are then put through cutting machines to make sheets and other shapes. Polyisocyanurate foams have excellent insulating value, good compressive-strength properties, and temperature...