Abstract: An improved process is disclosed for the preparation of a cured substantially closed cell phenolic resin foam by preparing a mixture of a foamable phenol-aldehyde resin, a blowing agent, and an acid catalyst, allowing the mixture to foam, and curing the phenolic foam, wherein the improvement comprises:(a) maintaining the water content of the foamable mixture below about 14% by weight,(b) using a resin-soluble acid catalyst,(c) adding at least a minimum amount of two parts per hundred resin of surfactant to the mixture prior to foaming, and(d) adding a member of the lactone family to the mixture prior to foaming.