Heat-transfer mechanisms in polyurethane rigid foam

Polyurethane closed-cell rigid foams have been widely used as insulants in the building and refrigeration industry and also for district heating pipes. It is the special combination of excellent insulation performance and the mechanical stability due to the foaming process which makes this material very attractive for these applications. The replacement of chlorofluorocarbons, which have been banned as blowing agents since 1993, by hydrocarbons in Europe caused a decrease in the insulation capability of polyurethane rigid foams. The additional global requirement to reduce energy losses also adds an incentive to search for potential substances which would improve the thermal performance of rigid foams. To overcome this problem the heat transfer within polyurethane rigid foams via the polymer matrix, enclosed gas, and thermal radiation was examined in various independent experiments. Most importantly, it was observed that the potential to reduce the thermal conductivity of polyurethane rigid foams is higher than had been predicted.