Abstract: A flame-resistant liquid absorbing paper is perforated to define small holes and is folded to form a box-like disposable liner bag having an open end and substantially the same dimensions as the heating and cooking chamber of a microwave oven. The liner bag is provided with fold lines for collapsing the bag to a flat condition for shipping and storage, and strips of pressure sensitive adhesive are carried by side walls of the liner bag for releasably attaching the bag to the microwave oven walls to maintain the open condition of the bag within the oven chamber. The small holes within the liner bag provide for release of vapor generated from a food item being heated or cooked within the bag and/or for air circulation within the oven. The liner bag may also be provided with an opening in the bottom wall for receiving a turntable or rotary platform within the oven chamber.