Injection moulding apparatus

Apparatus for producing an injection moulding of plastics material comprises means (18) for introducing a supply of plastics material (19) through one or more openings (43) in a mould space (13), and means (26, 34) for introducing a pressurised gas through a separate opening (44) in the mould space into the plastics material filling the mould space whereby the gas creates a gas containing cavity (25) in the plastics material and for thereafter relieving the gas pressure within the gas containing cavity before the mould is opened. The gas supply/pressure relieving means comprise at said separate opening (44) a valve port (42) opening directly into the mould space, a valve member (26) for opening and closing the valve port, and means (34) to supply pressurised gas to the mould space. The gas supply means are arranged to supply gas through the valve member (26) whilst the valve member is in a valve port closed position to create the cavity and after a moulding operation has been finished, the supply of pressurised gas can be terminated and pressurised gas in the cavity in the moulding can be vented to the atmosphere due to movement of the valve member to a valve port open position.