Subfloor panels are 20mm panels of unfinished material used to provide a flush floor foundation to support other surface materials, wall-to-wall carpeting in particular. They are usually made of a simple low cost material like plywood, wheatboard, fiber-cement panel, recycled HDPE, or even just cardboard. They can sometimes be used as a nailing foundation for other floor materials and with a recessed floor grid can support a cast light concrete or tile floor, but in general the Utilihab system rejects the use of nails and other non-demountable attachment.