A mat is a border, usually made from mat board, placed around the artwork. The
purpose of the mat is:

First, to provide a spacer or separation between the artwork and the frame or
glass. If the glass comes into contact with the art, there could be a risk of
damage to the artwork. This damage may come in the form of mold, or the
artwork adhering to the under side of the glass.

Second, the mat, particularly the color of the mat, draws the eye into the
picture. By altering the colors in the mats, we can make the colors in the art
stand out.  

Third, the mat hides the mechanics of the framed piece. For instance, the mat
will cover the mounting method used such as a hinge or dry mount.

The standard size of mats is 32 x 40, but some colors will come in an over-sized
40 x 60. The standard thickness of a mat is 4 ply, which is about 2 mm. Mats
are also made in a limited color range of six, eight and twelve ply thicknesses.
These thicker mats create a dramatic presentation, drawing the eye directly to
the art. Mats come in a variety of colors and textures which will allow your
design consultant to select the mats that just right for your picture.