Red rosin paper
Red rosin paper (red building paper, brown rosin paper, slip sheet paper, rosin-sized sheathing paper, and building paper) is a 100% recycled heavy duty felt paper used in construction such as underlayment under flooring and siding. The name "rosin-sized sheathing paper", commonly used to describe the material, comes from the rosin used in the paper, the process of sizing it to add the rosin, and its use by builders. "Alum-rosin size was invented by Moritz Friedrich Illig in Germany in 1807..." and is known to have been used as a building paper by 1850.
In building construction red rosin paper is used to reduce air and moisture flow through a wall or floor, create a "slip sheet" so different materials can slip by each other as they expand and contract, keep dust from working down through a floor, minimize squeaking, and sometimes as part of built-up roofs. Rosin paper is also temporarily used to protect a work site during construction. Rosin paper may have a polyurethane coating to improve moisture resistance and tearing. It is not acid free particularly containing abietic acid and comes in many size rolls up to 96 inches (2.4 m) wide.
Papers from the Middle Ages were sized with gelatine but the invention of the paper-making machine in the late 18th century demanded a better size  resulting in the creation of the rosin size.
A modern equivalent would be Synthetic Resin Bonded Paper (SRBP).
- Jim Thurn, "History, Chemistry, and Long-Term Effects of Alum-Rosin Size in Paper" The Cochineal December 3, 2003. quoting Barrow Research Laboratory, W.J.. 1974. Permanence/durability of the book-VII physical and chemical properties of book papers, 1507-1949. Richmond: W.J. Barrow Research Laboratory., and Green, S. 1992. "An outline history of sizing methods with special reference to practices at Hayle Mill". Conference papers manchester 1992, Third International Institute of Paper Conservation Conference, Manchester. 197-200. "Archived copy". Archived from the original on 2012-04-25. Retrieved 2011-10-09.CS1 maint: archived copy as title (link) accessed 3/11/2014
- Svensson, Inga-Lisa and Alwarsdotter, Ylwa. "A Papermaker's View of the Standard of Permanent Paper, ISO 9706", A reader in preservation and conservation. München: K.G. Saur, 2000. 62. Print.