Nice work on the pipe insulation holder. I do something similar.
The pins are from those little construction flags and are plastic. I am not sure what the foam is, but it is very firm and I used drill bits to fit. It may be used as draft/weather seal for congregated roofing/siding. It is on a Maximus Hunter which is my pester.
The silver highlights in the stock were done with a calligraphy pen I picked up at Walmart. It turned out really nice. I did all the grooves on the stock.