For use under a twin mattress when you don't want any lift, but need a good supportive base. This thing is solid as a rock and won't move. 2" or less profile - Mattress sits right on top of it. Perfect for bunk beds or a twin bed where you want the mattress to sit on the slats, but with more support and frame stability.
Sometimes these are called bunkie boards.
Piece is covered in an upholstery material and has always been covered with a thick plastic cover.
New and never used. Paid $300 for it and selling for $100 cash, firm.