Neil Stevenson, commercial director and UK MD of Grafityp, the UK partner for Siser, offers tips on how to overcome the problem of heat pressing decorations onto polyester

When faced with transferring designs onto materials that scorch with too much heat, even the most experienced of us encounter problems. Polyester is one such material. With many heat-susceptible products and other technical fabrics now so popular, we need to take extra care to reduce the chances of marking the garment or products we are working with. 

Hi 5, as used on this Russell garment, is designed for quick, low temperature applications

If you’ve been keeping up with Grafityp on social media you will have seen the numerous Siser blogs that offer tips and tricks on our Siser HTV materials and how to apply them on to all kinds of materials and textiles. A common question we are asked is, “How can I apply HTV on items that are heat-sensitive fabrics, like 100% polyester, silk, rayon, etc, where the heat press can often mark, leaving a square or rectangular impression all around the applied area?”

If the garment or textile care label specifically calls for ‘no iron’ or a ‘cool iron’, it’s most likely because the material will discolour under high heat settings. This is the first warning to take care. Sometimes this discolouration is only temporary, but other times it can be permanent. It’s always better to test a spare garment first, or test press on an inconspicuous area of the garment , so you know exactly what you are dealing with before you start. 

Heat press

First of all, you need to make sure your press is up to the job and working correctly. When working with heat-sensitive fabrics, making sure that you are using accurate temperatures and correct pressures on your heat press is a must. We have seen it many times before where customers think that their temperature is set correctly, but in reality, it can be very different on some older presses. Check it out first, because bad tools = bad job. Next, take a look at materials that can be applied at lower temperatures. Products that work with lower application times and/or lower pressing temperatures can eliminate those horrible press marks we all dread.

Another big problem with polyester fabrics is that they have often been coloured using a sublimation dyeing process. This can cause all sorts of issues when you’re trying to then apply your printed design onto it. The dye that was used to colour the garment will start to bleed when heat is applied: basically, the heat reactivates the dye that was initially used to colour the textile, which ‘migrates’ into the printed ink film. When faced with this type of issue it is imperative that you use the best materials possible to overcome this problem. Lower application temperatures or the use of materials containing chemical blockers are the best solutions. Siser products such as Hi 5 and Ink Block PS LT will dramatically help to reduce your stress levels when working on these difficult projects. Both of these products are available in Cad-Cut for standard cutting and in printable options for machines such as Roland and Mimaki printers using eco-solvent inks.

Taking cover

We always recommend a heat transfer cover sheet for all your presses. This heat barrier is especially important when pressing these heat-sensitive materials. Heat transfer cover sheets oer heat-temperamental textiles such as polyester a layer of protection from the hot upper platen on your press. If you don’t have a cover sheet you can use a parchment paper or the shiny side of multipurpose paper. It is also possible to use heat press pillows to raise just the area of the material that needs to be pressed; the heat press pillows are available in various sizes. This works very well but the technique can be a little difficult to begin with and requires some practice. Printing on polyester can be a challenge, but by following these pointers you can say goodbye to those sleepless nights dreaming about press marks all over your polyester garments.