Imagine a newly-printed polyester t-shirt, still warm from the heat press. The artwork you just added to the front looks vibrant and colorful—exactly what your customer wanted.

Then you notice the discolored border of scorched fabric around it. It’s the dreaded heat press box, and it means that shirt is effectively toast.

This sad scene happens to almost everyone working with polyester fabrics. But it doesn’t have to. By the time you’re done reading this, you’ll know what causes heat press scorching and how to avoid it.

Heat tolerance is a key factor

Solving the puzzle of scorched polyester starts with knowing a garment’s heat tolerance—a fabric’s sensitivity to high temperatures. Since polyester is a synthetic fabric, its heat tolerance is affected by when and where it’s produced, the dyeing process, and whether it has recycled plastics. As a decorator, you must adapt to these variations for a successful print.

Natural fibers like cotton don’t have this issue. The steam you see rising from cotton during press is moisture leaving the fabric. Any color change will balance back out as the cotton fibers reabsorb the lost moisture, usually over a couple hours.

But once a scorch sets in on polyester, it’s there to stay. Here are a couple tips to avoid this.

Always test first

Test your garment for its specific heat tolerance before going all-in.

For example, the wildly popular direct-to-film transfer has a relatively tight range for heat application. If you’ve already purchased or produced those transfers, you’re committed to the method. If the garment changes sheen at the needed temperature, you’re stuck figuring out how to make a bad situation look its best.

So, test first and adjust to a method that works for the garment.

Check every step

The best advice is to stop immediately if the first print doesn’t look right. The cost of changing your process is always less than redoing an entire order.

We’ve prepared a quick guide for every step of the printing process, from pre-press to inspections of the final product. Even if you run into trouble, there are some last-ditch efforts you can try—we’ve included those in the guide, too:

Better endings

Now imagine a different outcome: another polyester fabric on the heat press. This time, you tested beforehand and checked along the way. And voila!—no scorched fabric around the edges.

You beat the dreaded heat press box. You feel the pride in a job well done, and that sound you hear is a cash register, ringing up another successful sale.

May all your future polyester endeavors end like this.

If you have questions about using a heat press on polyester fabrics, or any other decoration dilemmas, the SanMar decorator solutions team is here to help. Contact us any time for recommendations or advice.