The baseboard has a light and strong assembly that can be dropped without damage. The outer frame is 1/4 inch x 3 inch ply with 1 x 2 inch pieces fixed to the inside providing a ledge on which the piece of 40 x 21 inch pink insulation sits on a piece of 1/8 inch plywood. I like to put a piece of ply under the foam in case I ever want tofix anything to the underneath. It is much easier to do this on ply than foam. I am beginning to work out where the retaining walls go.