Car siding, is a tongue in groove board, some times cedar, some times pine, with some decorative "v" cuts that adds some definition to the siding. I have seen it in either 6" or 8" widths, and lengths of 12 feet. The siding can be installed both vertical or horizontal. If horizontal, the tongue is usually on the top to avoid water retention & rot. This siding can be used both for interior "wood" rooms, and also for exterior siding. Staining or painting is also necessary.