It is well-known that the foamability of nonionic surfactants is reduced above the cloud point temperature. Above this temperature, the surfactant aqueous solution separates into two phases, a surfactant-rich phase and a surfactant-poor phase. The surfactant-rich phase plays the role of an antifoam. We show that the antifoam mechanism of action is the bridging of the foam films made with the dilute phase by tiny drops of the surfactant-rich phase which merge into the air-water surfaces of these foam films.