Topcoats are applied last to give the color, luster, smoothness and other cosmetic qualities to the vehicle. Topcoats must also protect these qualities over a long period of time from external factors (sunlight, rain, bird droppings, etc.). Topcoats may be divided into several groups as shown below.

This type of top coats is commonly known as lacquers, and is divided into NC lacquers, NC acrylic lacquers and CAB acrylic lacquers by the kind of resins used. Air-dry type topcoats have the following properties:

Topcoat where drying process includes a urethane reaction, which forms a net-like structure. The main agent and the hardener, are kept separate until they are mixed together just before application.
The urethane type dual-component topcoats are further divided into following three groups by resins type and drying time.

Acrylic Urethane Lacquer
Dual component acrylic urethane is blended with nitrocellulose to quicken the drying speed. It hardens when mixed with an isocyanate hardener. Nitrocellulose does not react with urethane hardener, and does not dissolve in solvent completely, so it is not suitable for quick repairs. Has been mostly replaced by quick dry acrylic urethanes.

Standard Acrylic Urethane
Commonly referred to as just ‘‘urethane’’ or ‘‘acrylic urethane,’’ this dual-component topcoat mainly consists of acrylic resins. It hardens when mixed with an isocyanate hardener. It has an outstanding coating performance, but dries very slowly unless force dried. It is suitable for painting large areas.

Quick Dry Acrylic Urethane
Often referred to as a quick-drying urethane. It is designed to shorten drying time without affecting the coating performance. Made mainly of acrylic resins and hardens when mixed with an isocyanate hardener. Commonly used for paint repairs because of its quick drying property and outstanding coating performance.

These are single-component type paints that harden when heated to about 284 °F (140 °C). Baked type paints that are used in vehicle production lines are also sometimes used for repainting.
Examples of baked type topcoats are shown below.

Thermoset Aluminum Alkyd
Also called melamine baked paint, this is a solid type paint mainly consisting of melamine and alkyd resins. Mainly used for solid colors.

Thermoset Acrylic
Metallic paint mainly consisting of melamine and acrylic resins.

A type of paint with a special water-based acrylic resin and very little organic solvent. This makes it more user and environmentally friendly. Because this type of paint becomes thinner when shaken or agitated, it is relatively easy to handle and especially suited for even application of metallic colors. When used with a solvent-based clear coat, the finish quality and workability are basically equivalent to acrylic urethanes.