Why Sublimation Paper Curls and Warps
Sublimation paper has a specially coated side designed to receive and hold sublimation ink until you press it onto a blank. That coating reacts differently to moisture and heat than the uncoated side, which means the two sides of the sheet expand and contract at different rates. When conditions are not right, this mismatch causes the paper to curl, bow, or warp, and that can lead to misaligned transfers, ghosting, and uneven colour coverage on your finished product.
Understanding why it happens is the first step to stopping it. There are a few main causes, and most of them are straightforward to fix once you know what to look for.
Humidity Is the Biggest Culprit
Sublimation paper absorbs moisture from the air readily, and this is the single most common reason for curling. Even moderate humidity levels can cause problems if the paper has been left exposed. The coated side and the uncoated side absorb moisture at different rates, which creates tension in the sheet and makes it curl, usually towards the coated side.
If you live somewhere with changeable weather or your workspace does not have climate control, you will likely see this problem more often during humid months. Printing with damp paper causes its own set of issues too, since moisture trapped in the paper can turn to steam during pressing and affect your transfer quality.
The fix is simple but needs to be consistent. Store your sublimation paper in a sealed plastic bag or an airtight container whenever you are not actively loading it into the printer. Throw a few silica gel packets into the bag to absorb any residual moisture. Do not leave an open pack of paper sitting on your desk for days or weeks at a time, especially in a room without a dehumidifier. If you have opened a pack and left it exposed for a while, you can sometimes rescue it by placing the sheets in a sealed bag with fresh silica gel for 24 hours before printing.
Paper Weight Matters
Lighter sublimation papers, typically around 90gsm or below, are more prone to curling than heavier options. They have less physical rigidity, so any moisture absorption or heat exposure warps them more easily. Heavier papers (100gsm and above) hold their shape better during both printing and pressing.
That said, heavier paper is not always better for every job. Thicker paper takes slightly longer to release ink during pressing and can sometimes leave a texture impression on soft substrates. For most standard sublimation work on mugs, coasters, and polyester fabrics, a good-quality 100gsm to 120gsm paper strikes the right balance between curl resistance and transfer performance. Our A4 sublimation paper is a popular choice that handles well across different conditions.
Coated Side Confusion
Sublimation paper has a bright, coated side and a duller, uncoated side. You print onto the coated side, then place that printed side face down onto your blank for pressing. If you load the paper the wrong way round and print onto the uncoated side, the ink will not be held on the surface properly. It soaks into the paper fibres instead, which means less ink transfers to your blank and the paper itself behaves unpredictably during the press, often curling or bubbling because the moisture and ink are in the wrong layer of the sheet.
Most sublimation paper brands mark the coated side in some way, either with a slightly whiter or glossier appearance, or with a small indicator on the packaging showing which side to print on. If you are not sure, run your finger across both sides. The coated side usually feels slightly smoother or tackier than the reverse.
Practical Fixes for Curling During Pressing
Even with properly stored paper and correct loading, you may still get some degree of curl once the paper has been printed and is waiting to be pressed. Wet ink on one side of the sheet changes the moisture balance and can cause the paper to bow. Here are the most reliable ways to deal with it.
Tape All Four Edges
Use heat-resistant tape to secure all four edges of the printed paper to your blank before pressing. This holds the paper flat against the surface and prevents it from lifting, shifting, or curling during the press cycle. Taping just one or two edges is not enough, as the free edges can lift and cause ghosting where the paper moves and creates a shadow of the design.
Pre-Press Your Blank
Before you apply your transfer, press the blank on its own for 3 to 5 seconds. This drives out any moisture that may have been absorbed by the substrate and also gives you a hot, dry surface for the paper to sit against. This is especially helpful with fabrics and any blanks that may have been stored in less-than-ideal conditions. A dry, pre-heated blank helps keep the paper flat from the moment the press closes.
Store Paper Flat
Keep your paper stored flat, not standing on its edge. Paper stored upright can develop a permanent curve over time as the weight of the stack causes the sheets to bow. Keep the pack lying flat in its original packaging, inside a sealed bag, in a dry area of your workspace.
Use Paper Promptly
Once you have opened a pack of sublimation paper, aim to use it within a reasonable timeframe. Paper that has been sitting in an open pack for weeks in a room without humidity control will gradually absorb moisture and become harder to work with. If you do not print in high volumes, consider buying smaller packs rather than bulk quantities that will sit around for months.
When to Replace Your Paper
If you have paper that has been left open in a humid environment for an extended period and it is visibly wavy or curled, it is usually better to replace it than to fight with it. Badly moisture-damaged paper will not feed through your printer reliably, and even if it does, the ink absorption will be uneven, leading to poor transfers. Fresh paper stored correctly from the start will save you time and wasted blanks. Browse our full range of sublimation paper to find the right option for your setup.