|I've seen many comments on the boards about pressing polyester fabric...they can't get their seams to press open, nice and flat. I think I know what the problem is....
Iron manufacturers may be erring on the side of caution. I sure know that my iron falls in this category. In other words, when they calibrate the temperature dial with the heating element, they choose to keep the heat lower, as opposed to as high as possible.
My iron has these settings:
 Acetate, Silk
 Acrylic, Nylon
 Polyester, Rayon
 Cotton Blends
If I set my iron on , it won't press 100% polyester worth a hoot. It's like I forgot to turn the iron on. I pushed the setting up to 4, then 4 1/2, and tested on scraps of my fabric [polyester satin charmeuse]. It pressed beautifully!
Testing is very important. Don't skip this test.
Tip...if by chance, your test scrap of polyester actually melts because your iron is too hot, just iron [hot iron] over a 'fabric softener dryer sheet' [new or used] to remove the gunk from your iron.