Binders also known as film former, resin, polymer, medium or varnish is that part of the paint which holds it all together. It contains the pigment, solvents and additives mixed within it and due to its physical and chemical properties, gives the paint its characteristics. Specific types of film former are often used to classify the end product e.g. alkyd, acrylic and nitrocellulose. They can be divided into two groups in order to more easily described the drying mechanism. Non-Convertible and Convertible Non-Convertible coatings are those that rely soley upon evaporation of the solvent to form the dry film, no chemical change occurs, so when dry they still remain soluble and will re-dissolve in their own solvents. In the refinish field, Belco-nitrocellulose, Belcryl acrylic lacquer and Ultra clear are in this category. Sometimes referred to as lacquer-dry types, they have the advantages of easy application, non-crytical recoat time and easy repairability. However, the high molecular weight polymers used require considerable quantities of thinners to give spraying viscosity, thus giving lower solids and build per coat. Convertible coatings are those that undergo a chemical reaction as well as losing the solvent during the drying process. The polymer becomes fully X-linked and totally insoluble when dry. Their lower molecular weight calls for less solvent to attain application viscosity, thus giving the advantage of higher solids at the gun. Application conditions and recoat times are more critical than the non-convertible types, but durability usually better.