A polymerizable composition is obtained by mixing a metathesis polymerization catalyst including benzylidene(1,3-dimethyl-4-imidazolidin-2-ylidene)(tricyclohexylphosphine)ruthenium dichloride, a cycloolefin monomer such as 2-norbornene or tetracyclo[6.2.1.13,6.02,7]dodec-4-ene, a chain transfer agent such as allyl methacrylate, and hollow particles such as Shirasu balloons. A crosslinkable resin composite is obtained by coating or impregnating the polymerizable composition onto or into a support medium, and carrying out bulk polymerization of the polymerizable composition. A crosslinked resin composite is obtained by crosslinking the crosslinkable resin composite.