The invention relates to an apparatus for controlling the composition of gases within a cargo container. The apparatus includes at least one sensor, at least one controller and at least one gas permeable membrane being adapted to facilitate the passage there through of different molecules at different rates. Said membrane defining a first region and a second region, the first region being for holding cargo and the second region defining a gas buffer region, said at least one inlet and/or outlet being in communication with said buffer region. The invention further relates to a container.