To form a superior finished surface by extrusion molding or injection molding by bringing at least two coaxial layers, namely a first outer layer composed of a generally used plastic material into contact with a second layer composed of plastic containing at least a filler for improving the soundproofing properties on one common face.

A composite wall of a pipe T is constituted of at least one outer layer 1 composed of conventional plastic and a layer 2 containing a filler C suitable for improving at least the soundproofing properties formed coaxially with the outer layer on the inner side of the radial direction of the outer layer. Also it is preferable to form a coaxial layer 3 composed of similar conventional plastic on the inner side. As the conventional plastic layer is formed, the polishing action of an injection molding machine or an extruder generated by the filler, particularly contained in the second layer being coextruded, is reduced during the manufacture. Also the superior soundproofing properties can be provided and the connection and bonding of the pipe and the formation of a joint are easy by leaving the outer appearance and the surface finish of a final product just as they are on a conventional pipe.