A multi-layer sheet for forming an expanded foam container, the multi-layer sheet including a first layer of an expanded foam material including a first polyolefin-based material including at least one polypropylene-based polymer and a second layer of an unexpected material including a second polyolefin-based material including at least one polypropylene-based polymer that is co-extruded, extrusion coated, or laminated on a first side of the first layer.

A large concentric co-extrusion die (1) is described having a plurality of annular or conical die mandrel layers (201-205). Each layer is formed between a pair of adjacent annular or conical die mandrels (101-106) defining between them a flow path for molten thermoplastics material from an inlet to an annular extrusion outlet (110) through which a thermoplastics tubular extrusion is formed in use. Extrusion takes place through the multiple annular layer outlets (301-305) to form a multi-layered product. At least one layer (203) of the annular or conical die mandrels has a plurality of molten material inlets arranged around the external circumference of the co-extrusion die with each inlet being connected to a feed channel (403) which has plural bifurcations (403.1, 403.2, 403.3) providing 2.sup.n subsidiary outlet feed channels (503) where n is the number of bifurcations. Each subsidiary outlet feed channel being connected to a corresponding helical outlet channel (703).

An injection head for an apparatus for the production of twin-wall pipes has an external melt channel leading to an external nozzle and an internal melt channel leading to an internal nozzle. From the internal melt channel, a conically expanding internal nozzle channel leads to an internal nozzle outlet of the internal nozzle. In the region of the internal nozzle channel, an internal nozzle adjustment device is arranged by means of which the gap cross-section of the internal nozzle channel is displaceable and adjustable up to the internal nozzle outlet by radial displacement.

A corrugated pipe manufacturing cell is configured to produce multiple corrugated pipes in parallel. The manufacturing cell may comprise an extrusion system that is capable of providing multiple independently regulated flows of plastic piping material to multiple die heads. The multiple die heads may feed a set of mold blocks having dual cavities for forming he multiple corrugated pipes. The pipe manufacturing cell may be converted between a first mode for producing large diameter single corrugated pipes, and a second mode for producing smaller diameter, plural corrugated pipes.

A laminated resin tube includes an inner layer containing a thermoplastic material which is a thermoplastic resin or a thermoplastic elastomer, an intermediate layer provided on the outer periphery of the inner layer and containing a polyamide, and an outer layer provided on the outer periphery of the intermediate layer and containing a fluoropolymer.