A method of forming an extrusion comprises passing a first, plastics material (12) through a first channel (104) in a die, passing a second, plastics material (14) through a second channel (112) in the die, and passing a third, plastics material (16) through a third channel (314) in the die. At least one of the materials is passed through a metering gap into contact with the other materials to cause the at least one material to bond with the other materials as the materials pass through the die.