Things You'll Need
Flat and heavy object (example: text book)
Creases in folded posters may not seem like a big deal, but they are unsightly and damaging. If a poster is folded for too long, the colors in the creases begin to fade until no color remains at all. Luckily, this can be remedied by a professional restorer. One way a professional might remove creases from a poster is to provide a linen backing, which positions the print so it lies flat, and smooth it out so that lines are minimized. If you don't have the money to hire a restorer, it may be possible to remove the fold lines from a poster using everyday household items.
Fold the poster in the opposite direction of the current creases.
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Open the poster, lay it on a flat surface and weigh it down with a flat, heavy object. It is not important that the object covers the entire poster, as long as the folds are weighed down. Leave them in this position for at least a full day, though two or more days are preferable.
Remove the weighted object, but keep the poster on the flat surface.
Cover the poster with a thin linen, such as a sheet.
Heat the iron to a low setting.
Iron the poster, keeping the linen on top to serve as a barrier between the heat of the iron and the print.
Check the poster periodically to ensure you are not making any burn marks.
If the poster print is valuable, it is advised that you seek the help of a professional.