The mechanical properties of hybrid reinforced rigid polyurethane (PU) foams were investigated with the reinforcing agent SiO2 and fibers. The effect of content of SiO2 and fibers and the effect of length of fibers on the properties of the PU composite foam were emphatically analyzed. The experiment results show that the tensile strength of the PU composite foam is optimal when the content of SiO2 and glass fiber is 20 and 7.8%, respectively. Furthermore, the reinforcing effect of glass fiber, Nylon-66 fiber, and PAN-matrix carbon fiber were compared and the results show that the tensile strength of the PU composite foam reinforced with 3-5% carbon fiber is optimal. (C) 2004 Wiley Periodicals, Inc.