Leftover building material from a previous construction project. Stored indoors to keep clean and dry. Primarily used in industry for blast-proofing walls. It could also be used to turn a room of your house into a faraday cage for electromagnetic isolation. A lot of folks use them on their trailers
Roughly 20 full sheets available. Still in new condition. There's some extra scrap metal pieces I can throw in for free. Sheet sizes are 48" X 96" - (4 X 8 ft.). These same sheets are listed on Grainger for $222.62 each.
I'm asking only $100 per sheet. Stop by and see them for yourself.