Overmat vs floating mount: which protects a print more

An overmat, or window mat, is a board with an opening cut in it. It sits over the print, and its edges overlap the sheet. The Canadian Conservation Institute (CCI) says the overlap should be at least 2 mm to 4 mm so the mat holds the work down [3].

In a float mount, the whole sheet sits inside the opening, with its edges visible. NEDCC recommends folded hinges (v-hinges) for float mounts, which it describes as the case where the edges of the sheet show inside the mat window [2].

In this guide, a float means a sheet mounted on the backing board and shown inside a window opening, which is the arrangement NEDCC describes for float mounts [2]. The Library of Congress does not define the term, so we assume it means the same thing. A sheet with no window mat at all is a separate case.

Both styles mount a print and protect it. They differ in how much of the sheet edge the mat covers.

The Library of Congress is direct: overmatting provides more protection than floating in the window [1]. Its page does not elaborate, so treat it as a stated preference and not a measured comparison.

NEDCC calls the window mat the standard mount for works on paper [2]. CCI says a window mat creates an air space that protects the image from direct contact with the glazing, and that during handling a mat provides support and protection from damage [3].

CCI Notes 11/5 does not mention floating a work in a window [3]. So the safest reading is narrow. The sources support the overmat as the default, and they describe what a float must do to be safe. They do not rank floating as equal.

In a float, the edges of the sheet are visible and not covered by the mat. That is the point of the style, since the viewer sees the whole sheet.

NEDCC says the object must be mounted on the primary backing board and never on the reverse of the window [2].

An overmat hides the edges under the mat overlap [3]. It also lets the window be sized to reveal the image, platemark, signature and title [3]. If your product shows a printed border or a signature, a window can be cut to include it.

Both styles need to keep the print off the glass. The Library of Congress says to ensure the object does not touch the glazing, using a sufficiently thick-ply window mat or spacers along the perimeter of the mat [1]. NEDCC says objects should never be in contact with the glazing surface, and warns about moisture condensing on the inside of the glazing [2].

With an overmat, a sufficiently thick mat provides the gap [1]. NEDCC says four-ply board may suffice, but thicker mats are required for large sheets [2].

A float needs the same gap. For a float, check with your framer whether the gap comes from mat thickness or spacers.

The table below sets the two styles side by side.

Both styles need the same board and attachment discipline. NEDCC recommends 100% cotton rag board and says to avoid foam boards, kraft paper, self-adhesive tapes and lignin-containing paper-based mat boards [2]. For the detail, see the pillar guide conservation matboard and mounting for framed prints and hinges, corners and adhesives for mounting a print. These sources are written for works of art on paper, so treat them as a quality reference and decide per product line how much of it to apply.

1. Note that CCI says a mat provides support and protection from damage during handling [3].
2. If the look of the sheet edge is the product, choose a float and specify v-hinges, which NEDCC recommends for float mounts [2]. Confirm the glazing gap method as set out above.
3. Ask your framer whether the frame depth can take a spacer or a thicker mat, and compare the options against photo frame profiles. This is practical advice, not a sourced rule.
4. Checklist for the brief: window overlap (at least 2 mm to 4 mm per CCI [3]), hinge type, how the glazing gap is made, and board grade (NEDCC recommends 100% cotton rag mat board [2]).
5. Write the choice into your order brief, as described in how to brief a frame or board order.

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1. Preservation Guidelines for Matting and Framing, Library of Congress. loc.gov (read 2026-11-08)
2. 4.10 Matting and Framing for Works on Paper and Photographs, NEDCC. nedcc.org (read 2026-11-08)
3. Matting Works on Paper (CCI Notes 11/5), Canadian Conservation Institute. canada.ca (read 2026-11-08)