What type of plastic material can one build up on polymer guns?

[AutoPistola]

I noticed Robar and a few others that actually build up some sort of polymer on top of a plastic frame. What do they use? Some special type of resin or bondo??:confused:

I'd like to build up a customized trigger guard.

[Dfariswheel]

They use very specialized plastic welding technology.

Very few resins or "Bondo" will stick to the engineering-grade plastics guns are made from.
They "build up" the parts by actually welding more plastic on much like steel can be welded onto steel to build it up.

[AutoPistola]

That's cool that they can weld plastic, but uncool that I cannot.