"Dirt bike and ATV fenders are usually made of low density polyethylene (PE). Polyethylene is known as an "olefinic" plastic, which literally means "oily" plastic. Polypropylene (PP) is another type of plastic in this family that is sometimes used on dirt bikes and ATVs. You can recognize these types of plastic by their slightly greasy feel. They usually have a slightly translucent appearance as well."
I was looking for a much more flexable plastic material that would work on the bike. Our beek tends to be on the rigid side to me. Not that this site has anything to used but the "process" of how you repair the material. Work the material.
I am almost certain that the are made on an injection molder. this would be a problem for the paint to stick- it will not. you can get colors to inject into the forms thought. Black, White, blue, green, just not your color perfect match.
I do not know just trying to throw ideas out there. Brainstorming!