Mat Board vs Mounting Board Differences

Two essential framing materials with distinct roles and specifications

Mat board and mounting board are both rectangular sheets of layered paper stock, and they sit side by side in every framing supply catalog. But they serve different purposes, are made to different specifications, and choosing the wrong one for the job can compromise both the look and the longevity of your framed piece. This guide explains what each material is, how they differ in composition and thickness, and when to use one versus the other.

Mat Board vs Mounting Board: When to Use Each

Mat board is a rigid paper-based board used to create the visible border around artwork inside a frame. It is manufactured in layers: a colored surface paper, a core of compressed pulp or cotton fiber, and a backing paper. The core is the layer exposed when you cut a beveled window, which is why most mat boards have a white or cream core that contrasts with the surface color. Standard mat board comes in 4-ply thickness at approximately 1/8 inch (1.5 mm) and 8-ply at approximately 1/8 inch (3 mm). The surface is available in hundreds of colors, from basic white and black to textured linens, suedes, and metallic finishes. Mat board is designed to be seen, so surface quality and color consistency are its primary specifications.

What Is Mounting Board?

Mounting board is a thick, rigid sheet used behind the artwork to provide structural support. It holds the art flat, prevents buckling, and serves as the backing layer that the artwork is attached to via hinge tape, corner pockets, or adhesive. Mounting board is typically thicker than mat board, starting at 2-ply and going up to 8-ply or thicker. It is usually available only in white, off-white, or black because it sits behind the artwork where its color is not visible. The key specification for mounting board is rigidity and chemical stability rather than surface appearance. Acid-free mounting board is essential when the board will be in direct contact with the artwork for years.

Material Composition: Standard vs Acid-Free

Standard mat and mounting boards are made from wood pulp that contains lignin and acidic compounds. Over time, these acids migrate into the artwork, causing yellowing, foxing, and the brown discoloration line sometimes called mat burn. Acid-free boards are manufactured from purified wood pulp (alpha-cellulose) that has been chemically treated to remove lignin and buffered to a neutral pH of approximately 7.0 to 8.5. The highest grade, cotton rag board, is made from 100 percent cotton fibers and contains no wood pulp at all. Cotton rag board is the standard for museum-quality framing because it is naturally acid-free, lignin-free, and will not degrade over decades. For any artwork with monetary or sentimental value, acid-free materials are the minimum standard.

Thickness Options and When They Matter

Mat board most commonly comes in 4-ply, which is thick enough to create a visible bevel when cut and rigid enough to stay flat in frames up to about 24x30 inches. For larger frames or a more substantial feel, 8-ply mat board doubles the bevel depth and adds stiffness. Some framers stack two sheets of 4-ply to simulate an 8-ply look at lower cost, but the double bevel line is visible at close inspection. Mounting board ranges from thin 2-ply backing sheets to heavy 4-ply and 8-ply support boards. For small frames under 11x14, a 2-ply mounting board provides enough support. For larger pieces or heavier art, 4-ply mounting board prevents flexing and bowing inside the frame.

When to Use Mat Board vs Mounting Board

Use mat board when you need a visible border with a clean bevel-cut window around your artwork. The mat board sits on top of the artwork, and its window opening reveals the image. Use mounting board behind the artwork as a structural backing. In a typical frame assembly from front to back, the order is: glazing, mat board, artwork, mounting board, and then backing board or dust cover. You do not use mounting board where mat board belongs or vice versa. Mat board is too thin and decorative to serve as a reliable structural backing for large pieces, and mounting board lacks the color range and surface finish required for a visible presentation layer.

Cost Considerations and Sourcing

Acid-free alpha-cellulose mat board costs a little more than standard wood-pulp board, and cotton rag, the top tier, costs a bit more still; mounting board follows the same pattern. When ordering from CustomPictureFrames.com, the mat and backing materials are included as part of your frame configuration, and you can select acid-free upgrades during the ordering process. For a small amount more per project, acid-free materials provide long-term protection that standard boards simply cannot match.

Frequently Asked Questions

Can I use mat board as a backing board?

Technically you can, but it is not ideal. Mat board is thinner and less rigid than dedicated mounting board, so it may flex or bow in larger frames. For small frames under 8x10, a piece of 4-ply mat board behind the artwork can work in a pinch. For anything larger, use proper mounting board or foam board for adequate structural support.

Is acid-free mounting board necessary for poster framing?

For mass-produced posters with no significant monetary value, standard mounting board is acceptable. The poster itself is typically printed on acidic paper, so an acid-free backing offers limited additional protection. For limited-edition prints, signed posters, or any piece you plan to keep for more than five to ten years, acid-free mounting board is a worthwhile upgrade.

What is the difference between cotton rag and alpha-cellulose board?

Cotton rag board is made from 100 percent cotton fibers and is naturally acid-free and lignin-free without chemical treatment. Alpha-cellulose board is made from highly purified wood pulp that has been chemically processed to remove acids and lignin. Both meet conservation standards, but cotton rag is considered the higher grade because its fibers are inherently stable and do not require chemical buffering to maintain a neutral pH.