We live in a split-level house in the midwest that was built in 1975. We are currently in the process of remodeling our lower level after dealing with substantial flooding around labor day. As we are getting ready to start the rebuild I decided that it would be nice to rip out the outdated paneling and wallpaper and I have noticed that between the wallpaper/ paneling layer and the drywall, there is a thin layer of something like melamine that seems to run all the way up the wall. Does anyone have any experience with what this is? What purpose does it serve? I have attached some photos for clarification.

 

Looks like they used scraps of glassboard as a shim. Rip it off.