A sheath for optical fibres comprises a compound sheath having an inner sheath of high modulus and density, and an outer sheath layer of low density material. The outer sheath layer may be of foamed polyethylene and the inner sheath of polypropylene, both conveniently formed by extrusion. Such fibre...http://www.google.com/patents/US5121901?utm_source=gb-gplus-sharePatent US5121901 - Sheathed optical fibres and method of installing such fibres
