A container closure comprises an annular region forming a counterface against which a gas permeable, liquid impermeable sealing element may be applied so as to urge the sealing element into sealing engagement with the rim of a container opening. The annular region comprises a gas pathway from an interior space opposite the container opening to the exterior of the annular region. The gas pathway may be of closed cross-section extending through the annular region. Alternatively the gas pathway may be of open-sided cross-section and provided in the counterface. Yet alternatively the annular region may comprise a washer, with the gas pathway provided at least partly in the washer and/or at least partly in the remainder of the annular region. A gas permeable, liquid impermeable sealing foil for bonding to a container rim is also disclosed.