OEM Fender Flairs: Plastic?

[99'Subourbon]

As the subject states - does anyone know if the oem fender flairs are plastic? I know they are yellow at the base, so I assume so.

 

[96C1500]

I want to say they're plastic, but they might be fiberglass. Haven't seen them off a truck in a while

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[michael hurd]

Reaction injection molded polyurethane.

 

[99'Subourbon]

Reaction injection molded polyurethane.

So it's part plastic?

Alright - well that answers my question enough; I just need to break the surface tension of the fender flares for krylon fusion to bond with it (sanding). Satin Black flares here I come.