The board can be slightly alkaline or have a neutral pH. The latter is recommended for matting photographic materials. A reliable supplier should be able to supply the technical specifications for the board. Board is generally available in two, four, and eight ply weights. As the work of art is attached to the backing board, the board needs to be of sufficient thickness to adequately support it. Four-ply is the minimum that should be used to provide adequate support to an average size work of art on paper.
Museums generally choose white or cream coloured boards.
Coloured boards of acceptable quality are available but the chosen board should be lightfast and not bleed in the case of accidental water damage. The purpose of the window board is to provide a space between the artwork and the glazing material. The window opening is usually cut with a 45 bevel to reduce shadows being cast. In the case of an overmat the edges of the mat must cover the edges of the work by at least 0.5 cm to ensure that the mat will adequately hold down the work. For a float mat a similar distance of at least 0.5 cm should be left between the beveled edge of the window and the outer edge of the artwork.