A filling composition comprises (A) a mineral oil having a kinematic viscosity from 80 cSt to 100 cSt at 40° C.; (B) a styrene-ethylene/propylene diblock copolymer; and (C1) a propylene/ethylene copolymer having a weight average molecular weight (Mw) from 5,000 to 200,000 or (C2) an ethylene/propylene copolymer having a weight average molecular weight (Mw) from 5,000 to 200,000. The filling composition is used as a filling composition in a buffer tube.