The rigid polyurethane foam includes thermally expandable fine particles disposed between two or more adjacent cells, so as to be exposed to the inside and/or the outside of a unit cell, and a filler which is dispersed on the surface of the thermally expandable fine particles and/or on the inner and/or outer surfaces of the unit cell. The cells of the rigid polyurethane foam can be small and uniform in size and can be highly insulating.