In plastics extrusion apparatus including a rotating screw in a cylinder forming a channel receiving solid material and eventually expressing it through a die, the channel comprising a feed zone, a melting and compression zone and a melt pumping zone, the improvement wherein a solids decompression zone is between the feed and the melting and compression zones which has increased unit volume relative to that of the feed zone, with the channel of the melting and compression zone communicating with the feed inlet through the decompression and feed zones such that solids are initially metered producing a starved condition so as to melt at substantially atmospheric pressure without filling the channel of the melting and compression zone until close to its end.