The extrusion head including a conduit with a central mandrel extending within the conduit for supporting an inner die portion of a set of dies that has inner and outer die portions. An upstream spider and a downstream spider are included, and each have webs supporting the central mandrel at axially spaced apart positions. The webs of the upstream and downstream spiders can have web portions that are axially offset from each other to promote mixing of polymer flowing through the conduit.