Printing on hoodies and sweatshirts is very common in the printing business, therefore is safe to say that all screen printers will print on polyester goods at some point in their career.
Printing on polyester goods is not so different then printing on cotton, but if not done correctly can be a disaster. To start off, when your garment is made up of polyester you will need special inks. For example if you are printing white ink on a 50/50 safety orange t-shirt, you will need to use white low bleed ink. If you don’t use the low bleed ink what happens is the pigments from the dye on the garment bleed into the ink and turn its color. So in the example, the ink would initially start off as white and after the shirt has run through the dryer the ink will turn a yellowish color. This happens because the orange from the shirt is mixing with the white.
Furthermore, when printing on polyester goods it’s always a good idea to preheat the garment. The reason I say this is because polyester has a tendency to shrink when placed under heat. If you are printing a 3 color job your shirt will shrink during every flash and your alignment will be thrown off. To avoided this, you can just flash the garment first, then go ahead and “print flash print” etc.
Finally, you should also be careful when throwing your shirt or sweatshirt in the dryer. Since polyester Is sensitive to heat, it will melt and burn away quicker. So if you usually run your dryer at a belt speed of 5.5 with a temperature of 1025 degrees for cotton, you might have to lower the temperature a bit and bump up the speed. This will avoid any errors when printing any custom t shirts or sweatshirts.