What changes when you use a double mat?

Name the two layers.

Here, the lower mat is the layer nearer the artwork. The upper mat is the layer nearer the viewer. Both can share an outside board size while having different openings. The upper opening is usually larger in this simple arrangement, exposing a strip of the lower board around the lower window.

That visible strip is the reveal. It is measured between corresponding window edges, not between the outside edges of the two boards. A double mat is not simply twice the border width and does not double the visible image area.

Calculate a rectangular reveal.

For an equal reveal r at every edge, upper window width = lower window width + 2r and upper window height = lower window height + 2r. The addition occurs twice because the reveal appears on both opposite sides.

For a lower window of 7.75 × 9.75 inches and a reveal of 0.25 inch, the upper window is 8.25 × 10.25 inches. With an 11 × 14 outside board, the upper layer’s left/right borders are 1.375 inches and top/bottom borders 1.875 inches. The lower layer’s borders remain 1.625 and 2.125 inches respectively.

Visibility still depends on the lower window.

The larger top opening cannot uncover a signature that the smaller lower opening hides. First decide and check the lower window against the actual paper and protected details. Then plan the reveal and the outside borders.

The diagram assumes aligned, rectangular windows and equal reveals. Unequal reveals, shifted layers, bevel geometry and cut-face definitions need additional specifications. The single-mat planner does not automatically generate a verified double-mat order or resolve those choices.

Check stack depth and manufacture.

Adding a layer increases the component stack. Confirm the actual board thicknesses, frame depth and mounting plan; do not infer millimetres from a generic ply label. Whether a given reveal or narrow border can be cut reliably depends on the supplier’s materials and process.

Our example proves only a relationship between rectangular openings. It does not certify adhesion, spacers, preservation suitability or the physical stability of a narrow strip. A framer should confirm the assembly and final cut dimensions.

Make both windows explicit.

An order conversation should name the outside size for each board, lower exact window, upper exact window, layer order, orientation and reveal. Confirm which dimensions the supplier will cut and which it will calculate. If a supplier instead asks for artwork size and a reveal selection, ask for the resulting exact windows before approving.