Just what its name implies, unpaintable plastic is plastic to which paint will not adhere, due to the chemical compositions of said plastic. This plastic is sometimes used on Transformers toys for structural reasons, due to its durability, flexibility, or resiliency.
The two most common plastics that are unpaintable and often used in Transformers are Polyoxymethylene(POM) and Polyamide(PA). The vast majority of Transformers toys have at least one mold that is unpaintable.
- Beast Wars Dinobot's beast forelegs, the piece at the back of his beast mode neck, his robot shoulders, and his robot thighs are unpaintable plastic.
- Armada Thundercracker's silver plastic is unpaintable, which is why his eyes are silver and indirectly why his face is painted red. (Thundercracker's face is usually silver, but so his eyes and face weren't the same color, his deco artist changed Thundercracker's face color.)
- The Ultimate Battle Optimus Prime -- Much of his red plastic, especially the upper arms, is made of unpaintable plastic. This is why the Autobot symbol tampograph was moved to his forearm.
- OTFCC 2003 Sideswipe -- See photo and caption to right.