Ironing out Posters

I recently ordered 3 posters from art.com that I will eventually be gluing to cardboard in order to hang in a trade show booth.

The posters arrived tightly rolled up and I have unrolled them facing down with a heavy object place on top in hopes of flattening them out. I remember someone saying there was a technique using a warm iron and a damp towel that would remove the creases and flatten it out.

I really don’t want to ruin these posters, and I’ve tried rolling them backward in the past with poor results.

Is there a quick and easy way to flatten out rolled up posters using a warm iron that someone has tried and knows works?

I’ve had success placing posters like that face down on the carpet, covering the back with a screen taken from my screen door, and using (lightly) a clothes steamer.

If you will eventually glue them to cardboard, why the need to straighten them first?

My own technique is to reverse roll them: roll them up in a tight tube the opposite way to what they were originally rolled up.

I would just put them on a floor or bed and put heavy objects on the corners. Or just hang them up on a wall temporarily. That will get most of the curl out.