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.