Abstract: A closure for a transportable container used in the transfer of materials to or from an enclosed process area is described. The container docks with a port in a wall of the process area forming a sealed connecting chamber which is sterilized by irradiation. Communication between the interiors of the container and the process area is then established. The closure has a collar and a lid, which portions are formed so that all the surfaces which form part of the connecting chamber in use are in the direct line of the sterilizing radiation, which is normally ultra-violet or pulsed white light radiation. No relevant surface is shadowed from the radiation. The lid may be formed integrally with the collar with a thin web separating the two to define a fracture line. The lid is provided with a grip which can be grasped from within the process area. Application of a pulling force to the grip causes the lid to be pealed away from the collar without the generation of particulates.