1,187,983. Liners for tobacco pipe bowls. DUCOMMUN Inc. 3 April, 1967 [23 June, 1966 (2)], No. 15137/67. Heading A2M. [Also in Division Cl] A tobacco pipe 10 having a bowl 12, provided with a smoke passage 15, is provided with a liner 11 consisting of an insert 16 consisting of any suitable porous material capable of withstanding a temperature of 1900‹C., e.g. ordinary graphite, and provided with an aperture 17 in the position shown; the insert having a coating 18 of pyrolytic graphite which may have a thickness between 0.5 mils and 15 mils, and beneath which there occurs a transition zone the characteristics of which change from those of pyrolytic graphite in the region immediately beneath the pyrolytic graphite outer layers to those of pyrolytic carbon in the region adjacent the pores of the substrate which pores are impregnated with pyrolytic carbon. For the preparation of the coated substrate see Division C1.