|When working on a wool jacket, I was having trouble getting the seams to stay pressed open flat. I would press them, but five minutes later they'd be springing back up again. I asked my tailoring tutor about it, and she said to press the seam open with steam, then switch the steam off, cover the seam with a press cloth to prevent it from burning (I just used a scrap of silk organza) and press with the dry iron until the seam dries out - it's the moisture that makes wool spring back. And it worked!
See here, seam before - pressed but still far too sproingy:
here, and after - pressed and staying open flat here.