An insert for a multiple component container includes a reservoir with an opening defined by a peripheral edge which, in use, is connected to a sealing element (20). In use, the reservoir and the sealing element define a substantially sealed space. The reservoir includes a stationary portion (2) and a movable portion (4), which is connected to the stationary portion and is movable with respect thereto by the action of gas pressure within the reservoir. A discharge opening (6) is formed in the movable portion (4) and a gas leakage path is provided in the reservoir wall. A valve member (14) is connected to the stationary portion (2) and cooperates with the discharge opening (6) and substantially seals it. The application of a greater gas pressure to the interior of the reservoir than to its exterior results in movement of the movable portion (4) away from the stationary portion (2) and thus in the valve member (14) moving out of sealing contact with the discharge opening (6).