Closed-cell water-blown rigid polyurethane foams and methods for their production

A method of making a rigid polyurethane foam having a closed-cell content of more than 80%, more than 85% or more than 88%, measured according to ASTM D6226-15, comprising reacting a polyisocyanate with a polyol composition in the presence of components comprising a catalyst and a blowing agent composition, wherein

• the polyol composition comprises at least 30% by weight, based on the total weight of the polyol composition, of (i) a polymer polyol having an OH number of greater than 260 mg KOH/g, wherein the polymer polyol comprises a dispersion of polymer particles in a base polyether polyol having a functionality of 2 to 6, an OH number of at least 300 mg KOH/g, and no more than 20% by weight of ethylene oxide units, based on the molecular weight of the polyether polyol, wherein the polymer particles are the reaction product of an ethylenically unsaturated composition consisting essentially of styrene and acrylonitrile, and
• the blowing agent composition comprising water in an amount of at least 80% by weight, based on the total weight of the blowing agent composition.