A composition comprises (A) a mineral oil having a viscosity from 32 cSt to 100 cSt at 40° C.; (B) a styrene-ethylene/propylene diblock copolymer; and (C) from 1 wt % to less than 5 wt % polystyrene having a weight average molecular weight (Mw) from 1,000 to 100,000. The composition is used as a filling composition in a buffer tube.