• Epoxy powders
These can be formulated to give very high gloss and smooth coatings with excellent adhesion, flexibility and chemical resistance. The main deficiency is a pronounced tendency to yellow at elevated temperatures or when exposed to daylight. In addition, on exterior exposure they chalk rapidly. However film integrity on exterior exposure is excellent. The curing of epoxy powders is an additions mechanism and no volatiles are released during stoving.

• Polyester powders
These powders have excellent outdoor durability coupled with high resistance to yellowing under ultra-violet light and have to be stoved at extended times and elevated temperatures compared with epoxies. Their general chemical resistance is somewhat lower than epoxies.

• Epoxy-polyester hybrid powders
These powders are a widely used class of thermosetting powders in which the epoxy resin acts as a curing agent for the polyester resin. Depending on the choice of resins and their relative proportions, the properties of the hybrid will lie between those of the pure epoxy and the pure polyester. The presence of the epoxy resin leaves this type of resin susceptible to chalking on exterior exposure.

• Polyurethane powders
Polyurethane powders are based on hydroxy-containing polyesters reacted with masked (or blocked) isocyanates. They provide good all-round physical and chemical properties as well as giving good exterior durability.