A rigid polyurethane foam comprises the reaction product of an isocyanate and a thixotropic composition. The thixotropic composition comprises: a first polyether polyoi which is aromatic amine initiated and has ethylene and propylene oxide end capping; a second polyether polyoi having a viscosity at 25° C. of from about 500 to about 15,000 cps; a third polyether polyoi having a viscosity at 25° C. of from about 18,000 to about 60,000 cps and a functionality of from about 5 to about 7; and a hydrofluoroolefin. The thixotropic composition has a viscosity at 25° C. of from about 350 to about 5,000 cps. A method of forming a composite article comprising a substrate and the rigid polyurethane foam includes the steps of providing the thixotropic composition, providing an isocyanate, combining the thixotropic composition and the isocyanate to form a reaction mixture, and applying the reaction mixture to the substrate to form the composite article.