Today, it more commonly designates cotton fibers, usually cotton linter. The fiber content of mat board is important because rag fibers are a stable material which is less likely to degrade and become acidic over time than other fiber types. This designation assures that the material was not acidic at the time of manufacture. By absorbing these acids, the alkaline buffer prevents them from reacting with the paper of the object causing brittleness and discoloration. This is the term used to describe the alkali-resistant portion of a cellulosic material which is a highly pure form of cellulose.
Native cellulose consists almost entirely of alpha-cellulose.
Therefore, in purchasing paper products description of the fiber base as alpha-cellulose generally refers to a highly purified fiber derived from wood. This is a good, all-purpose weight of mat board designed to give support and provide protection for art objects. In specific instances, however, other plys might be acceptable. Lignin is a natural component of wood that darkens when exposed to light. Its presence and that of other reactive chemicals negatively affect the resistance of paper to aging.