Home › Glossary › Framing and hanging terms › Mat board
What is mat board?
A mat (or mount) is a thin paper-based board with a bevelled window placed between the picture and the frame. It keeps the artwork from touching the glass, where moisture can condense, and the grade of board decides whether acid will stain the art over time.
Diagram: frame layers. Schematic, not to scale.
Grades of mat board
| Grade | Made of | Note |
|---|---|---|
| Museum board | 100 percent cotton fibre | The highest quality (WMAT) |
| Museum (rag) mat | Cotton linters with a cellulose core | Less expensive conservation grade (WMAT) |
| Conservation or archival board | 100 percent high-alpha cellulose | WMAT |
| Acid-free lined board | Recycled core with a treated liner | Acid can migrate to the surface over time (WMAT) |
| Older wood-based mats | Often acidic | Can cause mat burn, brown marks spreading into the art (WMAT) |
| Archival four-ply | Acid-free or buffered | Recommended by the Canadian Conservation Institute for works on paper (CCIP) |
Wikipedia describes the bevelled cut as keeping the mat edge from casting a shadow on the picture and says pastels, chalk drawings and photographs are especially vulnerable to touching glass. The Canadian Conservation Institute adds that a window mat leaves space between image and glazing and that artwork is attached with Japanese paper hinges, not glue or tape. Margin arithmetic is on the mat and border page.
Sources
- Wikipedia: Mat (picture framing) (fetched 2026-11-12)
- Canadian Conservation Institute (Government of Canada): basic care, works of art on paper (fetched 2026-11-12)
- Wikipedia: Picture frame (fetched 2026-11-12)
Figures from these pages are paraphrased and re-checked on 2026-11-12. Where two sources disagree, both figures are shown. Hardware and wall products vary, so follow the pack instructions.