A resin composition contains a resin component containing a copolymer of olefin and a comonomer having polarity and an ethylene-propylene-diene terpolymer. The resin component is cross-linked and the tensile stress at 19% strain is 2.0 MPa or less. The resin composition has a sea-island structure in which the copolymer of olefin and a comonomer having polarity is the continuous phase, and the ethylene-propylene-diene terpolymer is the dispersed phase.