These are made from 10mm MDF. I routed the holes with a round head router bit and then sculpted around these with some left-over silicone. Yes, silicone, and in spite of its good sculpting I’d never use the ordinary kind again. As I could’ve foreseen, the models took about 5 base coats until paint would stick to the surface. Spend a few Euros more and buy the kind that says explicitly that it can be overpainted, or leave it.