Short answer: A backing board is the rigid sheet at the back of a framed piece that supports the artwork and protects it from knocks and pollutants. Conservation guidance asks for acid-free, neutral-pH materials. Some guides describe two layers, a primary board the work is mounted on and a secondary board behind.
What two sources say about Backing board
| Source page | Publisher | What the page says |
|---|---|---|
| Matting and Framing for Art and Artifacts on Paper (Preservation Leaflet 4.10) | Northeast Document Conservation Center (NEDCC) | Separates a primary backing board, the cotton rag board the object is mounted on, from a secondary backing board placed behind it unattached for physical and thermal protection. |
| Matting and mounting guidance (Library of Congress Preservation) | Library of Congress | Recommends acid-free, lignin-free corrugated board with a moisture barrier, or corrugated polyethylene or polypropylene, at least 3 mm thick, as the backing. |
| Framing Works of Art on Paper (CCI Notes 11/9) | Canadian Conservation Institute | Describes the backing board as a separate neutral-pH board behind the mat for added protection. It suggests acid-free matboard or certain plastic and foam-core boards, and advises against masonite, corrugated cardboard and wood. |
Key points
- The primary backing board is the board the artwork is mounted on; the window mat is hinged to it. [1]
- A secondary backing board can sit behind it, unattached, for physical and thermal protection. [1]
- The board should be neutral-pH, acid-free and lignin-free. [1, 2, 3]
- One guide suggests acid-free corrugated board with a moisture barrier, or corrugated polyethylene or polypropylene, at least 3 mm thick. [2]
- Another guide says to avoid masonite, plain corrugated cardboard and wood behind artwork. [3]
- Backing board sits inside the frame rabbet together with the mat and glazing, and can be secured with points, brads or nails. [1, 3]
Backing board compared with Mat board
| Aspect | Backing board | Mat board | Source |
|---|---|---|---|
| Position | Behind the artwork. | In front, with a window cut-out. | [1, 2] |
| Main job | Supports the work and protects it from physical damage and pollutants. | Frames the picture and holds glass away from it. | [1, 2] |
| Typical material | Cotton rag board as primary; acid-free lignin-free corrugated or polyolefin board behind it. | Cotton rag or purified lignin-free board. | [1, 2] |
| Attachment | Artwork is hinged to it; a secondary board sits behind unattached. | Hinged to the backing board with gummed linen tape. | [1, 2] |
Where sources differ
The sources differ on corrugated board. The Library of Congress accepts acid-free, lignin-free corrugated board, while CCI Notes 11/9 advises against corrugated cardboard in general; the difference is likely purified versus ordinary board. Terms primary and secondary backing board are used by NEDCC only.
Questions to ask a supplier about Backing board
- [ ] What is the backing board made of, and is it acid-free and lignin-free?
- [ ] What thickness is the board?
- [ ] Does it include a moisture barrier?
- [ ] Is it a single board or a two-layer set?
- [ ] Can it be cut to the exact frame size?
Read next on this site
- Conservation matboard and mounting for framed prints: what the museum guidance says
- Frame materials compared: polystyrene, wood and aluminium
- Frame Size, Sheet, Back and Profile: Three Bands
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Sources: [1] Northeast Document Conservation Center (NEDCC), fetched 2026-11-12; [2] Library of Congress, fetched 2026-11-12; [3] Canadian Conservation Institute, fetched 2026-11-12. As of 2026-11-12. General information, not legal, customs or tax advice. Wording is paraphrased from the pages linked; your written quote and contract govern.