The material is polystyrene. Like the packing in a TV set, but much harder.
The floor (below) is in one piece. The addition of the open mesh floor is trivial - four screws attach it.
A small sheet of correx (left sticking out, below, for purposes of photograph) makes the varroa floor.
It is recyclable (Number 6) - but that's not a huge concern because I expect it to last 10 years.