Rigid Polyurethane Foam: What Makes it the Most Effective Insulant?

The fundamental mechanisms of heat transfer through rigid polyurethane foam (PUR) are discussed in terms of three distinct elements λ _g , λ _s and λ _r , where they represent heat transfer by thermal conductivity through the gas phase, solid phase and by radiation, respectively. Estimated values for λ _g and λ _s are given and, from the known λ -value of the PUR foam, λ _r is estimated by difference. However, there are indications that factors other than cell size affect the value of λ _r , giving scope — within the existing foam technology — to reduce the λ -value by a reduction in λ _r to its theoretical minimum. Using a novel polyol system in combination with high functionality isocyanates, the initial foam λ -value has been reduced by about 13% from its current level. Further optimisation to give foam with maximum insulation efficiency is in progress.