What kinds of plastic do Gunpla use?

I was reading a review of the Build Strike Full Package Gundam (https://gunpla.fandom.com/wiki/RG_GAT-X105B/FP_Build_Strike_Gundam_Full_Package) and it mentioned something unique in the notes. It mentioned that it would be a good idea to apply a top coat to areas with stickers on the “PP” parts. I’m under the assumption pp means polypropylene. I did not think Gundam used pp? Are there many kits that do and if so, why do the stickers not stick to it very well?

Have not really look at the tree parts of the instruction manual in detail for a while, but there were at least 3 kinds, maybe. PP, PS, and ABS. PP was most likely as you mentioned polypropylene. PS was probably polystyrene. And then ABS, not the braking system, but the acrylonitrile butadiene styrene. In fact, there was warning about painting on the ABS plastic in the color guide part of the manual and more apparent in the newer manual that have English.