A mat is a border of matboard used to enhance and protect artwork. Appropriate presentation of artwork with mat and frame makes the artwork more attractive and appealing, thus creating a more saleable product. Most shows and galleries require pieces to be matted and framed. Since paper starts as 99% water, art on paper is directly affected by conditions of humidity. Humidity has a lifelong effect on paper, causing it to expand and contract. If paper comes in contact with sufficient moisture, tide lines or even mold may develop. If paper becomes too dry, eventually the fibers may become brittle and if handled carelessly, may crack and break. Matting and framing provide a shield to protect artwork when handling. Artwork may be damaged by condensation forming on the inside of the frame's glass. This moisture is a result of temperature changes. Matboard separates the artwork from the glass and protects it from direct contact with moisture. But even properly framed artwork may be damaged when exposed to extreme conditions. When matting it is important to use acid-free matboard to prevent acid-burn which will yellow your artwork. Several brands of matboard are available at your local art or craft store.