Generally we recommend the use of Teflon sheets for heat transfer applications. The Teflon provides protection from direct contact with a press’ heating element and produces even heat distribution over the surface of the garment. But there are some thermal transfer applications for which Teflon is not such a good idea. In fact, it can ruin an expensive imprint. When should you not use a Teflon sheet for garment decoration? When you’re working with dye sublimation.
The thinner transfer papers used for dye sublimation serves only to carry the dye ink to the polyester. When the dye ink is heated to 400°F, the ink sublimates. It becomes a gas and bonds with the polyester fabric or the polymers of a coated substrate. But that’s not all that happens. If your transfer paper is saturated with ink--which is common if your SubliJET driver is set to “vivid”-- some of the ink may migrate through the back of the transfer paper. If you’re using a Teflon sheet, the end of that heat press cycle will produce a beautifully decorated garment and a not-so-beautifully decorated Teflon sheet.
This is only a slightly aggravating problem because at this point, all you have to do is A - replace the Teflon sheet or B - Make sure the imprinted area doesn’t touch an uncovered area of the next shirt you press. But as soon as someone carelessly uses that same Teflon sheet to press another shirt, your slightly aggravating problem becomes a costly production issue.
In the interest of Science I demonstrated this by sublimating one of our shirt samples with a Teflon sheet and pressing another shirt afterward. The first imprint looks great. (Fig 1, above) But it left a barely visible shadow image on the Teflon as the ink migrated upward through the transfer paper. The shadow is so faint, our Nikon D3 wouldn’t photograph it until I added a Bic pen to the area to get the picture (Fig 2). Although it’s too faint to photograph, it’s not too faint to ruin the next shirt.
In obedience to Murphy’s Law, I placed the Teflon sheet so that the shadow is outside the second shirt’s intended imprint area. Four hundred degrees and 40 seconds later, I had a custom imprinted, but totally unusable shirt. Hurray for Science! You can see the partial shadow of the top of the imprint a few inches above where the image is supposed to start, highlighted by the Bic shadow pointer-outer (Fig 3). So if you can’t use a Teflon sheet for sublimation, what can you use? How about a nice, fresh, sheet of copy paper? Just make sure it completely covers the transfer paper so you don’t have ink migrating to the bottom of the heating element. Use two sheets for extra security. They’re cheap and can be thrown away with the transfer paper after the shirt is done. (Fig 4). Your Teflon sheet is indispensable when you’re working with CAD heat transfer letters and standard inkjet transfers, but not with dye sublimation.