A microwave oven liner 11 is an injection moulding having a roof 12, a floor 14, a back 15 and two sides 16. The moulding is of food grade polypropylene, such that the liner can be washed in a commercial dishwasher. The liner is sized to be a sliding fit in a microwave oven. The roof is shorter 17 at the front than the floor to allow air circulation. Further, the roof is apertured, also for air circulation, with a series of small c. 4 mm bores 18 registering with the roof aperture 8. A lip 19 is provided across the front of the floor to retain split liquid. The external corners 20 are chamfered to clear the silicone seal 9 for instance. The floor has regularly pitched, 2 mm high ridges 21 running front to back. The ridges allow circulation of air beneath a container of food being heated in the oven having the liner.