An object of the present invention it to provide a novel fluororesin that has excellent mechanical strength and chemical resistance, and very low permeability at high temperature. The fluorine resin a copolymer that includes copolymerized units derived from tetrafluoroethylene, vinylidene fluoride, and an ethylenically unsaturated monomer other than tetrafluoroethylene and vinylidene fluoride. The fluororesin has a storage modulus E′, as measured at 170° C. by a dynamic viscoelasticity analysis, in the range of 60 to 400 MPa.