Abstract: The invention is based on the use of high-energy grinding mills for treating by combined mechanical and chemical action materials comprising one or more polymers in the liquid state thereof, in view of modifying the chemical/physical performance properties thereof. The polymers may be treated in the mill either alone or mixed with other materials, even non-polymeric organic or inorganic ones, which may themselves be either in liquid form or in the form of particles. An elastic transpiring membrane and an additive for protective coatings for wooden surfaces are specifically indicated and claimed as typical products among a variety of products that can be obtained with this method.