Surfactant for polyisocyanurate foams made with alternative blowing agents

A process for producing a closed cell, rigid polyisocyanurate foam which comprises bringing together under foam-foaming conditions a composition comprising a poly-isocyanate, a polyol, a hydrogen-containing blowing agent or a mixture of a hydrogen-containing blowing agent and at least one co-blowing agent, a trimerization catalyst, and a siloxane oxyalkylene copolymer as the surfactant, the siloxane oxyalkylene copolymer (i) having a weight average molecular weight below about 7500 and an oxyethylene portion containing greater than 60 weight percent of oxyethylene units and (ii) being prepared by the reaction of an organohydrogensiloxane with a polyoxyalkylene in an essentially solventless system or in the presence of a high boiling point polar polyol.