Sublimation file checklist: size, color and mirroring

Sublimation is unforgiving in a specific way. The print itself is permanent, bright and has no feel at all, because the dye becomes part of the material. But every mistake is permanent too. A pressed mug or shirt can't be reprinted, so a file problem costs you the blank.

Most wasted blanks come from the same handful of file issues. This checklist covers them.

How sublimation works, in four lines

The design is printed with special dye ink onto transfer paper. The paper is placed against the item and heated to around 400 F. The dye turns to gas and bonds with polyester fibers or a polyester coating. When it cools, the color is inside the surface.

Three facts follow from that, and they shape everything about the file:

• it only works on polyester or poly-coated items
• the dye is transparent, so there is no white ink
• the surface has to be white or very light

1. Build the file at the real size

Sublimation files should be made at the final print size, at 300 pixels per inch. Typical sizes:

• 11 oz mug wrap: about 9 x 3.7 inches, 2,700 x 1,110 px
• 15 oz mug wrap: about 9.5 x 4.5 inches
• 20 oz skinny tumbler: about 9.3 x 8.2 inches, 2,790 x 2,460 px
• Adult shirt front: up to about 12 x 16 inches, 3,600 x 4,800 px
• Mouse pad: about 9.25 x 7.75 inches plus bleed

Blanks vary by brand, so always use your supplier's template. If you sell digital designs, say which sizes the file fits.

Enlarging a small image to reach these numbers doesn't work. The print will be soft, and on a hard, glossy surface like a mug, softness is very easy to see.

2. Add bleed for anything edge to edge

If the design covers the whole item, extend the artwork past the edge by about 0.125 inch (3 mm) on each side, more for tumblers and all-over shirts. Blanks shift slightly in the press. Without bleed, you get a white sliver along one edge.

Keep text and important details at least 0.25 inch inside the edge for the same reason.

3. Treat white as "no ink"

There's no white ink in sublimation. Anything white in your design will simply be the color of the blank. On a white mug that's what you want. On a silver tumbler, a cream tote or a light grey shirt, your whites become silver, cream or grey, and every other color shifts with them.

This also means sublimation can't print light colors on dark items. For black shirts you need DTF, DTG or screen printing.

4. Decide: transparent background or not

For a design that sits in the middle of a shirt, a transparent PNG is best. Only the design transfers.

But check it carefully. A faint leftover haze from a quick background removal is invisible on screen and prints as a pale tinted box. View the file over a mid-grey background before you use it.

For full wraps and all-over prints, use a solid, flattened file that fills the template.

5. Get the color settings right

Color is where most frustration comes from.

• Design in RGB, normally sRGB. Sublimation printer software expects RGB and does its own conversion.
• Use the ICC profile for your ink and paper. Without it, blues turn purple and blacks turn brown or green.
• Don't judge by the paper. A sublimation print looks dull and washed out on the transfer sheet. The real colors appear only after pressing.
• Make blacks truly black. Set them to pure black in the file. A dark grey that looks black on screen presses as a weak brown.
• Press a test. A small swatch on the same kind of blank tells you more than any screen.

6. Mirror, or don't

Because the paper is pressed face down, the image has to be printed in reverse so it reads correctly on the item.

• Printing at home: mirror it, either in the file or with the "mirror image" setting in the print dialog. Not both, or it ends up the right way round on paper and backwards on the mug.
• Using a print-on-demand service: don't mirror. They do it. Upload the design the way it should look.
• Selling digital files: provide the design unmirrored and tell buyers to mirror when printing.

Symmetrical patterns hide the mistake. Text never does. Look at the printed sheet before you press: the words should read backwards.

7. Watch seams and wraps

On mugs and tumblers, the two ends of the design meet. Either leave a clean gap at the handle or back, or make the pattern seamless so the join disappears. A design that ends in the middle of a face or a word looks like a mistake.

On all-over shirts, expect small white creases at the seams and underarms. Avoid placing key details there.

The checklist

1. Polyester or poly-coated blank, white or light
2. File at final size, 300 PPI, using the supplier's template
3. Bleed added, important details kept inside the safe area
4. White areas checked against the real color of the blank
5. Transparent background checked for haze, or a full flattened wrap
6. RGB file, correct ICC profile, true black
7. Mirrored once if you print it yourself, not at all for POD
8. Seams and wrap joins planned
9. Test press on the same blank

The short version

Sublimation rewards preparation. The right size, clean transparency, honest whites and correct mirroring account for almost every good result, and their absence for almost every wasted blank.

If you have a design that's too small, has a messy background, or needs resizing to fit mug, tumbler and shirt templates, we can prepare the files for you. See our print-on-demand design service.