Abstract: The invention relates to an apparatus for continuous production of a strand of porous thermoplastic material from preferably pre-expanded granules of said material containing an expanding agent. The apparatus comprises an elongated rectangular channel, two opposite sides of which are formed by the horizontal parts facing one another of two superimposed endless belts moving in a closed path between turning rollers. The granules are introduced through the open intake end of said channel and are expanded to final size and sintered together to a porous coherent strand by means of steam fed between the horizontal belt parts facing one another. The steam and the granules are fed into the channel through individual ducts which are separated from one another and connected to the intake end portion of the channel. Usually, a plurality of granule feeding ducts and a plurality of steam supplying ducts are attached to the intake end portion formed as a box of particular shape.