Abstract: A low-density polymer composition and use thereof in undersea flotation cables and the like, the composition comprising by volume based on the whole composition,(a) at least 30% of a polymer component consisting of (i) thermoplastic polyolefin elastomer of room temperature density less than 0.9 g/cc and/or (ii) thermoplastic olefin/(ester or acid) copolymer elastomer, and(b) at least 30% of micro-balls of room-temperature density less than 0.6 g/cc, at least 80%, preferably at least 90%, more preferably at least 95%, by weight, of the micro-balls having a maximum dimension less than 300 .mu.m, preferably less than 200 .mu.m.Preferred elastomers are metallocene-catalysed olefin copolymers of density 0.86-0.88 g/cc, and micro-balls of diameters 10-45, preferably 10-34, micrometers are advantageous in resisting pressures up to 50 MPa (5 km under sea).