If you don’t lint-roll before pressing on polyester, you may end up with pesky blue spots. They weren’t there before you pressed, but after pressing they suddenly appear.
They’re actually dust particles that, when heated up, turn blue and are permanent. If you make it a habit to always lint-roll your polyester fabric, you won’t be bothered with this problem on your finished product.
-Cheryl Kuchek, Just My Imagination DeZigns