An isocyanate-reactive composition comprising (i) at least one isocyanate-reactive compound; and (ii) at least one T-shaped siloxane material at a predetermined amount; and a foam-forming composition for producing a polyurethane or polyisocyanurate foam comprising at least one isocyanate component and at least one isocyanate-reactive component; wherein the at least one isocyanate-reactive component is the above isocyanate-reactive composition.