Use for protective coatings of compositions comprising (% by wt.): A) from 10 to 60% of a A1) (per)fluoropolyethereal prepolymer having a polyisocyanic functionality obtainable by reacting a bifunctional having hydroxylic functionality, said fluoropolyethers having --CH.sub.2 OH terminations directly linked to a perfluoroalkylic group CF.sub.2 or CF.sub.2 CFX (X.dbd.Cl, F) or CF(CF.sub.3), with a polyisocyanate containing isocyanurate rings, preferably obtained by cyclotrimerization of HDI, IPDI or other monomeric diisocyanates, by utilizing an excess of isocyanate groups comprised between 10 and 80% by moles; the above fluoropolyether prepolymer can be partially or totally replaced by A2) non fluorinated polyisocyanates containing isocyanurate rings and/or hydrogenated polyisocyanate prepolymers;B) from 0.1 to 50% of a (per)fluoropolyether having bifunctional hydroxylic functionality of the type --CF.sub.2 CH.sub.2 OH, --CF.sub.2 CFXCH.sub.2 OH (X.dbd.Cl, F) or --CF(CF.sub.3)CH.sub.2 OH; or polyfunctional hydroxylic functionality termination but containing at least 5% by weight, preferably 10%, of the same type of termination indicated above for the bifunctional; or (per)fluoropolyethers prepolymers as defined in A) but having a lower prepolymerization degree so to leave free oxydrilyic functions of the type --CF.sub.2 CH.sub.2 OH, --CF.sub.2 CFXCH.sub.2 OH (X.dbd.Cl, F), or --CF(CF.sub.3)CH.sub.2 OH;or the latter prepolymers having free hydroxilic functions can be used alone as a single component, being component A) 0%;C) 10-90%, with respect to the resin of a diluting solvent.