Heats of immersion in water/7,, vr and in benzene H, .~ (in joules per gramme) of four silica fillers, modified by some silane coupling agents capable of forming polisiloxane network, have been determined by using a calorimetric technique. The Hi w and Hp values as well as strength properties (tensile strength, 200% modulus) of the sulfur-cured SBR filled with the examined silicas are predominantly a function of specific surface of untreated filler and of content of a given silane deposited on the silica surface. A direct correlation between heats of immersion hi w and hp (in J/m 2) and silane surface coverage has been also found. Moreover the wettability parameters determined in water and benzene can be useful for evaluation of filler activity in elastomer reinforcement.