Chapter X bibliography on rubber insulation 1951

It is characteristic of the present state of the science of insulating materials that the scope of any bibliography of rubber insulation should be somewhate ambiguous. Insulation containing Hevea is certainly rubber. Likewise nobody would take acception to placing GR-S, butyl, or any of the other “synthetic rubbers” in the same category. If butyl is a rubber, what of its blends with polyethylene? If they are rubber, is pure polyethylene also rubber? Where in this picture do we place plasticized polyvinyl chloride which is replacing rubber in many applications? If the meaning of rubber is narrowly construed then there have been relatively few new developments in this field during 1951. If it is broadly construed then developments are numerous.