Unpaintable plastic

Due to Prowl's mold layout, changing the outer shell of the car while leaving the limbs white for Sideswipe left a white part on the roof that had to be covered by a sticker. All of Sideswipe's white plastic (and the corresponding parts on other versions of the mold) cannot hold paint.

Just what its name implies, unpaintable plastic is plastic to which the type of paint Hasbro and TakaraTomy use will not properly 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 resilience.

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.

Examples

• 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 since his eyes and face would have been 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.
• Prime: Robots in Disguise Weaponizer Class Bumblebee has unpaintable plastic between his front wheels and doors, which is usually where his stripes would pass through. This is partly why his vehicle mode deco was entirely changed for the final product.
• Robots in Disguise Legion Class Strongarm's thighs. A paint operation planned for her kneecaps was removed due to this.
• Combiner Wars Dead End and his mold derivatives have unpaintable elbow joints. For Hasbro's versions of Dead End, Brake-Neck, Prowl, and Smokescreen, the elbow piece is molded in a color matching the car mode's side deco color, while the Unite Warriors versions of Dead End, Wildrider, and Prowl use plastic that matches the primary car mode color, as do both versions of Protectobot Streetwise and the Torchbearer Dust Up.

Photodegradation

While it is nothing new, it has become more prominent in products released in the War for Cybertron Trilogy toylines and several other lines released around this time. Several figures' unpaintable plastic has become increasingly susceptible to photodegradition as early as inside the packaging or about a week after being removed from the packaging. The colors of plastics that are known to fall victim to this, so far, are various shades of white, gray and metallic-gray/silvery plastic. These figures are also known to "yellow" even when they aren't left in direct sunlight, and have an accelerated reaction in humid climates, meaning that anyone living in a swampy area or in the Southern Hemisphere are more likely to see worse affects than someone living in say Canada or Northern America.

The leading theory among the fandom is that a fire retardant within the nylon chemical buildup is the cause of this and reacts to heat and/or humidity, causing the plastic to yellow. There was even one case in TFWiki.net's own community Discord server where the fire retardant chemical seeped out of a seam in an individual's War for Cybertron Trilogy Soundwave's knee! Gross.

Frequently documented victims include:

• Just about any version of the Megatron mold first released in the War for Cybertron: Siege toyline, that has either grey or silvery-colored plastics.
• Cyberverse Deluxe Class Arcee
• Studio Series Deluxe Class '86 Autobot Jazz
• War for Cybertron Trilogy Soundwave

Notes

• Yes, you can probably get commercially available hobbyist paints to stick to this plastic. You are not a multi-million dollar toy corporation and you are beholden to different budget constraints, not to mention your alterations do not have to hold up to the same testing and durability standards their mass-retail toys do. This fundamental disconnect is pretty much the entire driving force behind customizing.