The U.S. military began using polyurethane-based spray foam insulation in the 1940s on airplanes and rigid foams were widely used for ... for use in tight or hard to reach spaces due to its expanding ...

The first polyols used for rigid polyurethane (PU) foams were low molecular weight ... The polyether polyols proved to be superior in rigid PU foam fabrication, when the isocyanate index was low, ...