Abstract: A package is provided which includes a container having a chamber and provided with an opening which is closed by a multi-layered sheet. The multi-layered sheet is coupled to the container in hermetically sealed relation. The multi-layer sheet includes first and second layers in face-to-face relationship and cooperatively melded to the edge portion of the container. The first layer is adjacent to the container and obturates the opening of the container. The second layer is provided with a slit arrangement defining at least one displaceable flap. The first layer is imperforate and is relatively thin. It responds to a buildup of pressure within the container to rupture and displace the flap in order to vent the container. A third layer is further provided which is connected in face-to-face relationship with the second layer and which is also provided with the aforementioned slit arrangement.