Polyol blends and rigid foams with improved low-temperature R-values

A blend used to prepare polyurethane foams comprising:

• (a) 90 to 99 wt. % of an aromatic polyester polyol having a hydroxyl number within the range of 150 to 400 mg KOH/g;
• and
• (b) 1 to 10 wt. % of a C8 to C18 fatty acid ester selected from methyl soyates, methyl oleates, methyl palmitates, methyl myristates, methyl laurates, ethyl soyates, isopropyl palmitates, isopropyl myristates, hexyl laurates, sorbitan monooleate, sucrose monooleate, sucrose monolaurate, sorbitan monolaurate, sorbitan monomyristate, a C8-C10 methyl caprate/methyl caprylate mixture, a C12-C14 methyl laurate/methyl myristate mixture, C12 methyl laurate, a C16-C18 methyl palmitate/methyl stearate/methyl oleate mixture, PEG-400 dioleate, PEG-600 dioleate, PEG-400 diisostearate, PEG-400 dilaurate, PEG-400 disoyate, PEG-600 dilaurate or mixtures thereof, or a C8 to C18 fatty acid amide selected from N,N-dimethyl lauramide, N,N-diethyl lauramide, N,N-dimethyl myristamide, N,N-dimethyl cocamide, N,N-dimethyl palmitamide or mixtures thereof, wherein the blend is an unreacted mixture of components that is clear and homogeneous having a viscosity less than 5,000 cP at 25° C.