Moulding

A method for producing a shaped article which comprises extruding a thermoplastic polymeric material, initially in a molten state, through a die having a mandrel for constraining the material into a tubular shape and producing thereby a tubular extrudate having an outer surface and an inner surface;

• coextruding between the die and the outer surface of the polymeric material, a liquid having a freezing temperature lower than that of the polymeric material;
• cooling the liquid and the outer surface of the polymeric material during their passage through the die, to a temperature below the freezing temperature of the polymeric material but above the freezing temperature of the liquid, while maintaining the inner surface of the polymeric material molten;
• squeezing the extrudate at suitable intervals to fuse the molten inner surface together and thereby seal discrete lengths;
• and inflating a sealed length to conform to a surrounding mould, thereby to produce the shaped article, characterised in that the method is applied to a thermoplastic material containing a filler, the ratio of filler to thermoplastic material being at least 15:85 by weight, and that the sealed length of extrudate is moulded into an article with two closely-spaced substantially parallel walls enclosing a volume therebetween, a foamable composition is injected into the enclosed volume and the composition is allowed or caused to foam while the article is held within a constraining means constructed to prevent outward displacement of the spaced-apart walls by pressure from the foaming composition.