There is disclosed a container that is useful as a sterilization chest for surgeons' instruments and the like. The container includes a generally open-top box having a peripheral flange about its top edge and an open channel extending along at least two of the opposite sides of the box in the peripheral flange. A flexible membrane cover is provided which overlies the top of the box and the peripheral flange and this membrane is reinforced with a plurality of stiffening members which are supported on the undersurface of the flexible membrane cover in a side-to-side array. These stiffening members have distal, downwardly dependent lips which are received in the open channel grooves in the peripheral flange whereby the stiffening members reinforce both the flexible cover and the upper sidewalls of the box, preventing collapse of these elements when the chamber within the chest is evacuated. The flexible cover serves to seal the container yet it can be readily removed by lifting from a corner and, in this fashion, also serves as a valve for the sterilization chest.