An (A) additive organopolysiloxane composition is disclosed which comprises (A1) a branched organopolysiloxane polymer comprising M, D and Q siloxy units and (A2) a silicone resin. The (A) additive organopolysiloxane composition has a content of aliphatically unsaturated groups of from 1.5 to 7.0 wt. %. A curable composition is also disclosed, the curable composition comprising the (A) additive organopolysiloxane composition, (B) an organosilicon compound having at least two silicon-bonded hydrogen atoms per molecule, and (C) a hydrosilylation catalyst. A method of preparing the curable and a method of forming a film with the curable composition are also disclosed.