Abstract: A composition for protection of the liquid surface from heat- and mass-trfer, for example from evaporation, contains a polymer limitedly swelling in the protected liquid or a mixture of said polymer with a neutral filler having a density lower than the density of the protected liquid.A method for protection of the liquid surface from heat- and mass-transfer comprising application of said composition on the surface of a liquid, for example petroleum, in an amount of from 0.1 to 2 kg per m.sup.2. Upon contacting of the polymer with the liquid the polymer rapidly swells and forms a continuous gel-like covering which hinders the heat- and mass-transfer on the liquid surface.