Heat transfer vinyl is a fantastic material. With it, you can customize virtually any fabric surface (and even more). It’s one of the materials that lots of folks purchase a Silhouette machine to cut. But there are some myths floating around about how to use it properly. There are also problems caused by operator error. Today, we’re going to talk about what happens when you overheat HTV.
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Heat transfer vinyl is a polyurethane material with a heat-activated adhesive on the back. It typically comes with a carrier attached to the front, except on some printed HTV. Those have a carrier on the back and you use a transfer media to move the product to your project. It’s the adhesive we’re talking about today – what NOT to do to it and what happens when you overheat it.
For a primer on HTV, see this post.
When applying HTV, there are 3 variables: temperature, press time and pressure. If you have too much of one or more of those you overheat the adhesive, which weakens it. That means that it’s going to cause adhering issues in the long run. Let’s talk about ways HTV can get overheated and tip-offs that it is.
If the HTV isn’t sticking, turning up the heat or pressing longer
That’s very much a newbie mistake. We tend to think automatically that if the HTV won’t stay on, our iron isn’t hot enough or we aren’t pressing long enough. So we turn up the heat or press longer. I actually scorched the t-shirt on one of my first HTV projects because I did this.
The time and temperature recommendations of HTV manufacturers come from extensive testing. Since they make it, they know what they’re talking about. Using a higher temperature or a longer press time will actually keep the adhesive from doing its job in the long run. It will weaken it, or even cause it to evaporate.
So what is the cause of HTV not adhering? Usually, it’s inadequate pressure rather than too short of a press time or too low of a temperature. Here are some causes of poor pressure:
- Using a home iron on an ironing board. It has too much “give” so doesn’t provide a firm enough surface. You want to use something like a countertop or concrete floor. Of course, protect it from the heat with a towel or metal cookie sheet.
- Using a home iron without pushing down hard enough. It’s tricky to get used to how much pressure it takes when you first start out. Usually, it’s too little pressure.
- Uneven surface. This is especially true on things like baby onesies or around the seams of garments. The iron or heat press comes into contact well with higher/thicker parts, but not with the lower/thinner parts. That’s why you need to use pressing pillows or a rolled up towel under the garment to equalize the thickness. The thicker parts sink in and the thinner parts are get raised.
Repressing from the back side of the garment
This is a mistake I used to make and even advised people to do. I heard it from someone else and it seemed to make sense to me. So, I’d turn my t-shirt inside out and press again from the back side for a few seconds. But again, doing this can overheat the HTV and weaken it.
Pressing each layer of a multi-color design for the full time
When you’re using several colors of HTV on a single project, you can’t press them each for the full length of time. If you do, by the time you get to the 3rd or 4th color, the first one has been heated way too long. You also risk shrinkage, which makes it hard to get your pieces to line up.
Instead, use a “flash press” for all but the last layer. That means to press for just 1-3 seconds – just long enough to enable you to remove the carrier. On the last color, press at the lower end of the full time.
Pressing different varieties of HTV at the same temperature
If you’re mixing varieties of HTV, they often use different temperatures. For example, glitter HTV usually needs a higher temperature than smooth. First press the ones that use the higher temperature, then turn down your iron or heat press for those with lower temperatures. Or if you’re trying to press them all at once, split the difference on the temperature.
Adhesive creeping out from under the HTV
Have you ever seen a “halo” of adhesive around your HTV on your garment? You can see it around the darker pink on this t-shirt.
That comes from the adhesive becoming too liquidy when heated. Instead of staying between the material and the garment, it seeps out. That’s caused by too much heat or time. If you use a heat press, an extremely firm pressure can also cause that little outline of adhesive around your HTV.
Stiff feel to HTV
When you overheat HTV, it affects the material as well as the adhesive. It gets more of a stiff feel to it, particularly on large pieces.
The bottom line
Here’s the bottom line. Always follow the manufacturer’s directions for your brand of HTV. If you have problems with the issues mentioned here, do some testing on an old t-shirt. Maybe the temperature gauge on your heat press isn’t right. Perhaps you aren’t using the right amount of pressure.
Here’s a great video from Siser North America that talks about overheating HTV (it’s where I got all the info for this post). They have lots of great videos on their Facebook page and their YouTube channel that are well worth your time to watch. And my friend Joe Piazza who’s on most of the videos is super fun to watch.
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