The present invention relates to a method for providing a product viewing window in a container. The container has at least a body ply and a liner ply, wherein the body ply has at least one aperture therethrough. The liner ply is adhered to the inner surface of the body ply and has a portion extending across the aperture, forming a window into the container. The method involves providing a window-finishing machine that comprises at least two platens and, optionally, a machine pocket positioned between them, a heating element extending through at least one of the platens, and a pressurized air device that is adapted to release pressurized air into the container through at least one of the platens. The container is engaged between the platens in an airtight manner and, optionally, the container window is positioned adjacent the inside wall of the machine pocket. The heating element heats the window of the container to the desired temperature, pressurized air is injected into the container such that the window is forced at least partially through the aperture of the container (and optionally into contact with the machine pocket wall), and the container window is then cooled to the desired temperature.

An apparatus for supporting heating elements of a thermoformer oven includes a first heating element support frame, a second heating element support frame, and one or more actuator. The first heating element support frame is operable to support one or more of the heating elements on a first side of a surface for supporting material to be thermoformed. The second heating element support frame is operable to support one or more of the heating elements on the first side of the surface. The one or more actuator is configured to shift the first and second heating element support frames toward one another in directions with vector components of motion parallel to the surface.