Abstract: An apparatus comprising in combination (a) an elongated bundle of flexible, relatively small diameter, thin walled hollow polymeric tubular elements of various lengths, in a twist configuration having a length greater than the housing and a lateral dimension securing means at both ends, (b) a housing means for said bundle wherein said bundle extending entirely within said housing means with said bundle anchored to said housing means in said twisted configuration, (c) means for securing in fluid tight arrangement said housing means to said lateral dimension securing means and (d) circular spacers for the tubes, the longer length of said bundle when secured within said housing means causing a bowing of said tubes that permits flexing and moving of the tubular elements in said bundle.

Abstract: Hollow plastic filaments, useful in heat exchange systems, which are made from plastic compositions containing 5 to 45 percent by weight of filler particles having substantially higher thermal conductivity than the plastic and a diameter greater than 2.0 microns, will have high thermal conductivity and appreciable mechanical strength if the particles are chosen such that the ratio of the particle diameter to the wall thickness of the filament is between 0.001 and 0.5 and if the particles are dispersed within the plastic homogeneously enough to produce the desired mechanical stability and heterogeneously enough to take advantage of the high thermal conductivity of such a dispersion.