Method of producing rigid polyurethane foams with low thermal conductivity.

A method of producing a rigid polyurethane foam, closed cell, having a density of from 0.032 to 0.064 g / cm 3 and k-factors of less than 0.161 cal / h cm ° C to 24 ° C, which comprises reacting a) a isocyanate-reactive component comprising: (1) a polyol initiated polyether amine and (2) a polyester polyol and having a residual water content of less than or equal to 0.3% by weight, b) di- or polyisocyanate in the presence of c) a hydrofluorocarbon blowing agent, d) a catalyst, e) a surfactant, at a rate of diisocyanate about 1.0 to about 3.0, and whereby water is not added to the reaction mixture foaming.