A foam containing a nitrile group-containing conjugated diene copolymer and a urethane polymer, wherein relative to 100 wt % of the sum of the nitrile group-containing conjugated diene copolymer and the urethane polymer, the nitrile group-containing conjugated diene copolymer is present in an amount of less than 90 wt % and the urethane polymer is present in an amount of more than 10 wt %, the nitrile group-containing conjugated diene copolymer contains ethylenically unsaturated nitrile monomer units in an amount of more than 31 wt %, the foam has a density of 0.08 to 0.30 g/cm3, and in observation of an arbitrary cross section of the foam, air bubble cross sections present in the cross section have an average diameter of 350 μm or less, and the number of air bubble cross sections with a diameter of 0.6 mm or more present in the cross section is 0.062 per mm2 or less.