as to force the cable 24 into abutment with the outer wall 20 as indicated by the zone 34 the pliability of the cable 24 causes a slight deformation at the abutment ensuring a substantial contact area between the cable 24 and the wall 14 over the length of the conduit 10 to produce the conduit 10 the pipe 12 and cable 24 are fed into an extrusion die shown schematically in fig4 at reference numeral 40 feed stock for the jacket 30 is fed from hopper 42 into the extrusion cavity 44 to form the jacket 30 continued movement of the pipe 12 and cable 24 conjointly through the die allows the jacket 30 to solidify and provide the construction of the conduit 10 the finished conduit can be coiled depending on the dimensions of the pipe 12 or delivered in discrete lengths with suitable terminating and power connection kits applied to the cable 24 at the end of each length in operation the conduit 12 can be installed on a surface or within shallow trenches the jacket 30 protects the cable from external damage but does not impair the integrity of the structure of the pipe 12 at the same time the extended contact area ensures that the heating effect of the cable 24 is maximised and distributed to the fluid within the pipe 12 the voids 32 provide additional area in which heat can be conducted into the surface of the pipe through air contained within.