Abstract: A novel refractory fiber thermal insulation and a "wet pack" moldable insulation package formed thereof are described. This composition comprises refractory fiber having combined therewith a binder system comprising 25% to 95% by volume of an aqueous suspension of colloidal silica having a solids content of 15 to 30 weight percent and wherein the mean particle diameter of the silica particles is not greater than 10 nm, 5% to 12% by volume ethylene glycol, and 0% to 70% by volume additional water. Wet packs using this binder composition have significantly greater strength, better thermal properties (particularly at elevated temperatures) and better adhesion to metal surfaces than commercial prior art wet packs.