Well, I found it instantly this morning to quote the price, and just now blew my entire lunchtime trying t find it again.
Anytime I've bought them in the past, I just walked into a Home Depot and asked for "shower board, marker board, the cheap laminated particle wood". There are typically a few types, more like a board, so I ask for the flimsy ones used for cheap showers, and they take me to a stack of them in the lumber area. They are very thin, like an eighth of an inch. You'll need a vehicle larger than a sedan, BTW, this are BIG. But you can also have them cut for you, often no charge.
