Yep, drafting cloth, drafting linen, same thing. It's very good stuff, and I suspect it was withdrawn as a consequence of its expense. I encountered my batch at an old factory that was built in the 40's for manufacturing war materials, though I'd also seen it in many older engineering facilities. Most of the original architectural and structural drawing files for the facility were still housed on-site, and the storeroom contained a fairly large quantity of the old drawing cloth, so my supervisor gave me access to some for my personal use.