Abstract: A gelled oil filling compound primarily intended for optical cables which meets the standard drainage test at 70.degree. C. and is stable to prolonged exposure at -40.degree. C. consists essentially of a low aromatic hydrocarbon oil and a block copolymer with a molecular weight in the range 200,000 to 2,000,000. The block copolymer comprises at least one segment tending to confer solubility in the oil and at least one segment tending to inhabit it, the preferred example being the polymer sold under the trade mark KRATON G1651 which has a center segment which is a random copolymer of ethylene and butylene and two end segments consisting essentially of styrene units.

Abstract: A low-tack, non-cell-filling filling medium for telecommunication cables comprises 70-98% liquid base, 1-15% of a block copolymer and 1-15% of a dispersed phase former. The base may consist of a hydrocarbon or hydrocarbon mixture whose molecules are substantially incapable of diffusing into polyethylene, polypropylene or (with or without wax) other cellular insulating material at temperatures of up to 80.degree. C. or it may be a mixture of a mineral oil with a hydrocarbon or hydrocarbons satisfying the foregoing condition and also being soluble in the oil and having a low enough (number average) molecular weight to reduce significantly the osmotic pressure of the medium. The block copolymer includes at least one block tending to confer solubility in the base and at least one block tending to inhibit such solubility, so as to have a strong tendency to form a gel with the base.