What's the point of backing boards?

[alxs]

I've got about 15 large movie posters that need to be stored, most of them 27x41, one of them is 60x40, all of them unfolded.  Assuming I put them all in mylar sheets and lay them flat on top of each other in a drawer, what purpose would backing boards serve? 

Furthermore, lets say I decided to sandwich them all between two backing boards, as this guy shows.

http://filmschoolrejects.com/features/movie-poster-storage-ideas.php

If I put every poster in a mylar sheet, do I need to get acid free backing boards?  Will the acid from the boards literally eat through the mylar and harm the posters?  Or if each one has its own sheet, could I just get two large pieces of cardboard and sandwich them in between and be just fine?

[paul waines]

Don't worry too much about using backing boards, I stack my posters in a flat file on top of each other with no problems. As long as you don't have any problems with the posters...Tape, or stains etc, they should be fine.  If you want to go that step further just use the sleeves on their own, No need for backing boards, if your laying them flat.

And Welcome to the forum.

[CSM]

I like backing boards. But I only lay my posters flat.  I would never stand them upright for storage as this would no doubt result in a nicely curved poster and board!

[AdamCarterJones]

Exactly what Paul said and what Chris said...def don't stand them up.

Welcome to the forum, too!

[MoviePosterBid.com]

http://filmschoolrejects.com/features/movie-poster-storage-ideas.php

backing boards are neutralized. Not for forever, but for years.
will they help posters flatten over time if stored as sandwiches? sure they will.
I don't use boards and I don't bag my posters (it does not make them easier to handle, quite the opposite) what I do is lay a poster on foamcore in my flatfile, and then put in a plastic bag, another poster, plastic bag.
the weight of the bag is better than any other medium and it caresses the posters in all spots, unlike a stiff cardboard
it's worked for me for decades

I don't bag my posters. I don't bag & back them.

as to the link above.. I think it's one of many good ideas

[movieposterodyssey]

If you have a flat file you don't need a board or sheet for every poster. As said, you can just put a board inside and lay them on it. Then put mylar or another board on top.

If you don't have a file... bagging each would be best. Keeping dirt and insects away...ect. That "sandwich" method with acid free boards would work if ya had to. Stay away from cardboard! You don't want that cardboard box or any cardboard near your posters. Best to play it safe. I believe bagsunlimited has a acid free cardboard storage box you might be able to use. But regular cardboard...no.