a closure assembly is disclosed which includes a plastic sealing ring having an annular channel in it for receiving and sealing against the entrance mouth of a container , a metal foil liner spanning the sealing ring and a flexible plastic overcap which receives the sealing ring and foil liner therein . the foil liner has a heat seal coating on one or both faces for sealing to the sealing ring and , in some packages , to the plastic overcap . the three - piece closure assembly is positioned on the entrance mouth of a container and the foil liner is induction heated to soften the heat seal coating thereon to seal the liner to the sealing ring . induction heating may also be employed to adhesively join the foil liner to the undersurface of the overcap and seal the sealing ring to a foil layer in the container body .