A spider in an extrusion die mandrel has a plurality of internal plastic flow passages extending axially through the spider and a spider leg between each flow passage. Each spider leg has a region with a radially extending air passage and further has upstream and downstream spider parts to opposites sides of the air passage region. The upstream part is a flow splitter which splits flow of plastic along the die mandrel to the spider leg into a plurality of independent plastic streams which then flow around the air passage region in the spider leg. The downstream part of the spider leg has a plurality of flow guides staggered at different radial depths in the spider leg with all of the flow guides being directed at one another to guide the bonding of independent plastic streams after they have passed around the air passage bearing region of the spider leg.
