Inverse opal having mesoporous silica walls has been synthesized using close-packed polystyrene beads and octadecyltrimethylammonium chloride as a templates, and tetramethoxysilane as a silica precursor. The synthesized bimodal porous silica was characterized by XRD, N 2 sorption, SEM and TEM. Hollow silica with inverted opaline structure had a macroporous diameter of 390nm and a wall thickness of approximately 30nm, and the mesoporous silica walls had a specific surface area of 367m 2 /g, a mesopore diameter of 2.9nm and a wall thickness of 1.8nm. The refractive index (n) of this material was found be 1.05, which is lower than that of silica (n=1.44) and also close to that of the air.