The so -called reversible coatings are formed and created on the basis of these polymers, they can dissolve in organic any solvents. The simplest example of such polymers is nail polish. But the polyurethane paints after processing with their solvent are irreversible coatings, and therefore they do not dissolve at all or dissolve poorly. Irreversible coatings are always more rigid and hard than reversible. Irreversible coatings are obtained on the basis of completely different polymers, which are called stitched or metro. The polycondensation reaction of this kind of molecules occurs followed by the release of water, as well as other side substances. Glyftal and pentifal resins obtained from glycerol belong to such polymers.