Heavy paper impregnated with rosin, usually available in rolls 48"-72" wide. In the construction industry, it is used as a roofing or flooring underlayment. In theatre, it is most often used under backdrops while painting.
RED ROSIN PAPER
See this thread: https://www.controlbooth.com/threads/scrim-painting-issue.12079/ .
RED ROSIN PAPER
See this thread: https://www.controlbooth.com/threads/scrim-painting-issue.12079/ .