Wallpaper paste it to some light weight wood...I don't know...I'd have to look, but I'm thinking luan like the skin they use on hollow core doors. Or mod podge it on. It's not like it's something precious that needs gentle handling. Cut the wood to either fit the poster or leave a narrow margin of wood showing around it.

See, eg this from Home Depot.

I used these for a Longwood marketing poster that was about the same size.

https://www.wearewellmade.com/products/premium-magnetic-framing?variant=45476893720812

eta: i didnt realize 70” was the width nvm my suggestion unless it could hang vertically.

I've done the same as Spanish in the past -and the posters came with hangers on the back of the foam board - I didn't have to mess with it. Very light weight and honestly, even though they are essentially covered in heavy plastic wrap, they held up for a long time - like a couple of decades - without tearing.

lf you want a frame, get acrylic instead of glass, much lighter.

I third the notion of foam board. have them glue half inch or so battens on the back in a rectangular formation that will make the piece easy to sit on a nail (at least two for that one to keep it straight) and it will oroject out from the wall for a more pleasing and polished looking effect.

And framers do this?

You might even be able to take it to a print shop, I think my colleague took our group’s poster to Staples or Office Max/something. I think Michael’s will do it, too.

Yes they will all do it except places like proper art galleries

I bought my frame with acrylic instead of glass in the size I needed at Hobby Lobby. It was already premade.

I think this one was done at Michaels or Aaron Bros. It hangs in my bathroom with no window and has been knocked off the wall a couple times by moi. That’s how we got the divots at the bottom. Otherwise it’s still in great condition.

Its been in there since 2012.

hmmm ...... mat/foam backings are restricted to standard maximum industry dimensions (usually capped under 60 inches)

Just a wild idea - would DD consider cutting the poster into equal size sections, framing and hanging side by side? I realize in cutting and framing you'd lose some of the detail.

Yes ^^^ A diptych or triptych!

Prob not... though its a good idea

The one @jojoco linked goes in one inch increments farther than 70”.

In my old office, we had an architectural rendering of the building. It was about 18-24” x 72”; beautifully and professionally framed in a very simple silver-leaf frame with glass (in other words, it was heavy). I never saw the backside of it, but one of the older guys who was there when it was hung told me that the back side was a mass of reinforcements to keep the frame from sagging in the middle on the longer sides. The point of this ramble, consider sagging if you have a span of 70” .

This was my parting gift from me to me when I left Longwood. It is quite tall (51”)but not very wide. I had it framed at Michael’s with acrylic and even then it was about $400. The receipt said originally it would be $1100 but lucky me they were running a sale. As if! Felt like one of those perpetually going out out of business sale scams. But I do love it and I’m glad I had it done.It makes me smile every day.

Foam core? I did use styrofoam to create a long valance once....I used toothpicks covered in white glue to use as "pins" to hold the two pieces together, jamming the toothpicks halfway into the end of one and then shoving the next one onto the tooth picks. A bit of a pain, but it worked. I was covering it in fabric and batting though which is forgiving of any imperfections...poster might not be as forgiving...

If you want a framed option, for a very long time, I used Frame USA because I needed certain sizes and rabbet depth. They were a great company to work with. They have poster frames, and, yes, you want acrylic vs glass on a piece this size. This company won't even sell glass above a certain size. I'd just call their customer service, tell them what you have, and ask for their suggestions.

Professional framers may have a larger machine for dry mounting. If you recall these in our last house. 48" wide each (52" with frame), and as you can see, much taller. Dry mounted, framed and installed by a TTT only framing business. Somewhere someone can mount your daughter's piece..

This is a rather large(2'x4') "photo" I had printed, my husband took....then I purchased a LARGE frame(glass-matting-frame)....took the old photo out...put MY photo in. The frame, with the glass and gold border was $18.....from a Goodwill Boutique store. Yes...your right...it's heavy....just a thought...