There's often a flat piece of board at the bottom of the frame packaging, and it's usually the last thing you think about. Yet it determines whether your poster looks like a picture in a frame or art on a wall. The mat - the board frame between the print and the glass - is the cheapest way to elevate a poster to the next level, and at the same time, the most misunderstood. Get the measurements wrong and you'll crop the image. Choose poor quality and you'll get a yellow strip along the edge in five years. This buying guide covers what you actually need to know before you order.
Three functions of a mat - and you'll only notice the third
The obvious function is aesthetic. The mat creates a quiet zone between the image and the frame, giving the eye time to settle before it meets the wall. Without that zone, the brain reads the frame and the image as a single object. With it, the brain sees the image first.
The second function is mechanical and comes down to millimeters. A standard mat, around 1.4 millimeters thick, keeps the print a safe distance from the glass. It may sound fussy, but when moisture condenses on the inside of the glass - which happens in any room where the temperature fluctuates, especially against exterior walls and in hallways - it's the contact between the printed surface and the glass that causes damage. The ink sticks to the glass and comes away when you open the frame. That damage can't be repaired.
The third function is chemical, and it's the only one you won't notice until it's too late. A mat made from cheap wood-fiber board contains lignin, the same substance that makes old newspapers turn yellow. Lignin breaks down into acids that migrate into the paper it touches. The result is the yellow-brown outline left by the frame that you recognize from framed posters at flea markets: the image in the middle is unchanged, but right where the board touched the paper, there's a dark line.
Quick facts: Aging-resistant board compliant with DIN ISO 9706 must have a pH value between 7.5 and 8.5, be buffered with calcium carbonate, be lignin-free, and be made from 100 percent alpha cellulose. The industry's three recognized quality certifications are ISO 9706, the Library of Congress standard, and the British Fine Art Trade Guild's classification - if none of them are listed, the board is likely made from lower-grade wood fiber.
How to measure from print to frame without cropping the image
The most common mistake is ordering a mat with the same inner dimensions as the poster. Then the edge of the image sits exactly at the edge of the opening, and because the board always has to overlap the print slightly to hold it in place, a white strip shows on one side as soon as anything shifts by a millimeter.
Instead, allow for overlap. The opening should be about five millimeters smaller than the poster on each side, meaning one centimeter less in both height and width. If you have a 30x40 poster, the opening should be 29x39. It may seem negligible, but it’s the difference between an edge that looks intentional and one that looks sloppy.
Then choose the frame size. The combinations established in Sweden and available ready-made are easy to remember: a 30x40 frame with an opening for 21x30, a 40x50 frame with an opening for 30x40, and a 50x70 frame with an opening for 40x50. Each size up gives you about five to seven centimeters of mat board all around, which is the classic museum proportion.
If you want to go beyond standard sizes, order a custom mat, and there’s a framing rule worth knowing. The eye doesn’t perceive the geometric center as the center - it centers an image slightly higher than it actually sits. That’s why framers have made the bottom margin wider than the other three for generations. Traditionally, the bottom margin is about 25 percent wider, making the subject feel stable instead of slowly sliding down. Modern framing has softened the rule to just a few millimeters on smaller sizes, but the principle remains: if one side is to be widest, it should be the bottom, never the top.
"The mat is the only part of the framing whose job is not to be seen - and the only one that ruins the whole when it is."
White, off-white, or colored: why galleries almost always end up making the same choice
There’s a reason museums and galleries use off-white or pure white for almost everything. A neutral mat board recedes visually. It registers as air, not as a color surface, so it doesn’t compete with the subject for attention. As soon as the mat has a color of its own, it becomes a third player in the picture, alongside the subject and the frame.
The difference between pure white and off-white is still worth taking seriously. Pure white works best with graphic motifs, modern design, and black-and-white photography, where the crisp white reflects the print and enhances the contrast. Off-white or a light cream tone goes better with warm motifs, reproductions of older paintings, and anything with a paper-like quality - pure white around a warm-toned reproduction makes the print look yellowed, an effect you never notice until they’re side by side.
Colored mats aren’t forbidden, but they require a decision. They work when the color picks up a tone that’s already in the image and appears in at least one other place in the room. A black mat is a special case that works surprisingly well with black-and-white photography and subjects that already have deep tones, but it requires a thin frame profile to avoid looking heavy. What almost never works is matching the mat to a piece of furniture: the furniture gets replaced, but the poster stays.
Tip: Place the poster on the kitchen table and try an ordinary white A3 sheet beside a yellowish piece of paper, such as the back of an envelope. Slide them up against the edge of the image one at a time. You’ll immediately see which shade of white makes the print look clean - and it takes thirty seconds instead of several weeks of anxiety after a wrong order.
The wide mat: 2026’s clearest framing trend
If there’s one clear direction in framing right now, it’s generosity. Industry trend roundups for 2026 point the same way: wide mat borders that emphasize the empty space around the subject, rather than maximizing the image area. The idea is that a small subject in a large frame with a wide mat is read as something valuable - museums have used this technique for a hundred years, and the effect is that viewers slow down.
You can take it a long way. An image in 13x18 centered in a 40x50 frame creates a dramatic effect that works on a narrow wall where you only have room for one thing. The subject becomes a focal point, not a surface, and the room around it does the work. The same logic is behind more people choosing large formats with generous mats instead of filling the wall with lots of small pictures - a trend that also appears in how gallery walls are built in 2026, where the overall effect matters more than symmetry.
But there are cases where a mat does more harm than good, and they’re easy to identify. Images composed without a margin - full-bleed photography, motifs where the color extends to the edge, large abstract areas - lose something when framed with a mat, because the whole point is that the image doesn’t end. There, frameless framing is the right choice. The same goes for hanging several posters close together in a grid: a mat around each image creates so much white space between them that the group falls apart. And in very small sizes under 21x30, a wide mat can easily look comical - the image shrinks to a postage stamp.
Quality tiers and what they actually cost you
Mat board comes in three broad tiers, and the price difference is smaller than most people think. The simplest tier is regular wood-fiber board with a white surface, often without a stated standard. It works for a poster you plan to replace within a few years, and for the constantly rotating pictures in a child's room, it's a perfectly reasonable choice.
The next tier is acid-free mat board that meets ISO 9706. It's buffered, lignin-free, and labeled, and it's the obvious choice for anything you want to keep. The price difference compared with the simplest tier is often ten to twenty kronor per sheet in standard sizes - less than the cost of shipping.
The top tier is called museum-grade or conservation-grade and is made entirely of alpha cellulose or cotton rag throughout, not just on the surface. You need this grade if you're framing something irreplaceable: a signed print, an heirloom photograph, an original. It's overkill for a printed poster, and honesty requires saying so plainly in a buying guide like this.
The same applies to the glazing. Standard glass or acrylic is sufficient in most rooms, while UV-filtering glass is worth the money on a wall that gets direct sunlight for part of the day. We cover how light in a room affects both color and viewing experience separately in our guide to the effect of light on art on the wall, and it's worth reading before you decide on the type of glazing.
If you're buying a frame and mat board at the same time, it's easiest to start with the size. Our most common sizes are 30x40 and 50x70, and in our frame selection you'll find wooden and metal mouldings to suit both. For an overview of choosing a moulding, see the guide on how to choose the right frame for the right poster.
Frequently asked questions about mats
A mat is rarely more than a fraction of the frame’s cost, yet it’s the detail that determines whether the result looks like a product or something you chose. Start with the measurements, stick to a neutral color if you’re unsure, and spend the extra twenty kronor on labeled acid-free board. The rest is about the image - and you’ll find it in our full range of posters, whether you’re looking for graphics, photographic art, or something that simply makes the wall feel complete.