I have a few posters I’ve been storing for some time, that have been somewhat creased in that time. Not enough to make “crease lines” so to speak, but enough so that they bend when opened and don’t look flat on the wall. Most of them are tolerable, but the one that has the most visible bending is a bullfight poster I bought in Spain. It is composed of a thinner, more crinkly paper than the other posters (which are made of that smoother, glossier poster paper, if you know what I mean), which reminds me a bit of the brown paper you might wrap a package in. Is there any good way to flatten it/them out? The only thing I could think of would be leaving it open between two pieces of cardboard that take up the whole area and pressed down by some heay books. I also thought of ironing, but I assume that would present a high risk of burning the paper? Is there anything else I can do? I really like this poster and would like to be able to put it back up.
You can iron paper on a low setting (no steam) - if you’re nervous, place a towel on top of it. Always iron the back of the poster.
If you hang the poster those creases will drop out over time (God bless gravity).
You could also get it mounted onto cardboard, coreflute or some other backing.
Fang, when I saw the title of this thread, I thought, “Fella, I’ve got a long list of Posters I’d like to flatten!” 
Seriously, turn the iron down low, put a thin piece of cloth between the iron & the poster, & check frequently & carefully.
Very good thread, nice job Fang.
Ohhh, I thought you said Flattering the Poster
I had one of those bullfight posters too, they are very nice. The last time I moved, when I opened it up it crumbled into a million pieces. I would say if you want to keep it a long time, it would be a good idea to have a pro frame and seal it.
And here was I thinking, “Oooo. What a title, and only two replies. I’m in with a chance!”
Curse you Bosda!
Just tack it down
That generally works for me
I hang them, and put large size binder clips on them as weights. This is reasonable if you work in an office and they’re readily available, but not so much if you have to buy them.
On a related subject, is there any way to safely flatten a photocopy? I´d be a bit reluctant to iron it.
Place it on a flat surface and stack a couple heavy books on top of it. In a couple days gravity will do the work for you.
I always take my posters to the local art store and they dry-mount them for me. Basically, they adhere each poster to rigid quarter-inch-thick foam that keeps the poster flat and smooth. If your poster doesn’t have any bad creases, dry-mounting may eradicate any minor wrinkles it already has. Dry-mounting isn’t too expensive, either.
Drymounting is a heat-application process which puts a double-sided sticky layer between poster and backing - heat, melt, stuck. You can even do it on photos, no worries.
I´ve kept the photocopies in question pressed for the last 6 months and the darn papers still curl up…