They look like they were printed with an FDM printer (the type that basically works like a super fancy, amazing hot glue gun) so it was probably PLA (polylactic acid) or maybe ABS. The laser-cutter's a bit different since it takes a sheet of material (as opposed to an FDM printer which would take filament which is like a "string" or "wire" of plastic). I just haven't had the time to look into it since there are limitations on the plastic you can use in the laser-cutter. One of these days...Yeah, he is using some newer plastic material which is very firm yet has some give. I tested out with a plain, sanded version (the above is not sanded) over the weekend, and it worked great! I forgot the name but I'll find out and report back when I share the next rev of this.