Using XPS Foam Board for Props

Archived Thread
Our site is currently being changed over to the new version. Everything you see is currently in read-only mode. Additionally, the layout and UI will not be complete until all sections have been re-enabled, so please ignore any layout issues (or bland-ness) at this time.
#1 PermanentSky on 1 year ago

It is my first time using XPS foam (I think that's what it's called, here is an image of what I'm using: [url][/url]) and I will be carving out a staff from it ([url][/url]. I plan on layering two 1" pieces together for thickness and carving from there. I am unsure of how to paint it. From what I found online, I know not to use spray paint directly, as it will eat away at the foam, so I will be using acrylic paint. In the past, when I have used EVA foam, I had to seal it with a heat gun and some other primer. I was wondering if I had to do the same with XPS foam or is there another method I should follow to get a smooth texture for painting?
Also any tips on working with XPS foam would be greatly appreciated!
Thank you!

#2 Midnight Dawn on 1 year ago

I would suggest against insulation foam. Aside from health hazards, smoothing it is going to be a real pain.

Are you limited on what kinds of tools you can use? Otherwise I would suggest you use different materials for several of the pieces of the staff such as wood, plastics, and/or eva foam.

#3 Penlowe on 1 year ago

Eh, if you've got a good dust mask and can work outside it's not so bad. That stuff creates a sand like dust when cut so it's best not done over carpet or near food, or indoors at all if you can help it. If you must work indoors, even a garage, have a vacuum cleaner present and on with the hose close to your cutting to keep the fine dust under control.

If you are only using it for the staff head, sure. Don't use it for the rod, it's not strong enough.

Sandwich something not as brittle as the foam in the center, like cardboard. Foam can snap off with a clean break, cardboard will hold your pieces together. The foam will still break if whacked, but at least it'll be a cracked prop instead of a broken one.

Smoothing it by itself is dreadful, but it will take plaster slurry or thick gesso fairly well. Those two products will seal the foam from paint issues as well as give you a sandable smooth surface.

Personally, I like plaster, but it has a learning curve, and it's way messier than gesso. Like clean up with the garden hose before going in the house kind of messy.

#4 nathancarter on 1 year ago

That pink or blue foam board is extremely fragile and unsuitable for a standalone material for a prop. it's great for adding lightweight bulk to a prop that needs to be large, but it will need an internal reinforcement as well as an external coating or shell of some sort.

I used it to make a skull helmet. I built it over a comfy ball cap, glued layers together for thickness, and carved it down. For the delicate parts (horns and mandibles) I made a center core out of MDF; for the delicate tips of the bone parts I drove a glue-covered rigid wire (coat hanger) into the foam; then I covered the whole thing with several layers of paper mache, then sanded and filled and sanded and painted.

If you use it for the wings of your staff, at a minimum you'll want a center core of cardboard, but something sturdier like MDF, styrene, or Sintra PVC sheet will be stronger. Without such a reinforcement, those wings will snap off as soon as the wind blows the wrong way, let alone trying to navigate a crowded convention with it.

Starting to carve the shape:

Building the horns around a core of MDF:

Covering with paper mache:

Final look after sanding, filling, sanding, detailing, painting:

#5 KuruttaKanashii on 1 year ago

I used a technique recommended by the Homestucks to make two-foot-tall helmet horns for Lord Dominator. I shaped the foam the way I wanted, covered it in paperclay, sanded it smooth and painted over that. The horns smacked into a bunch of stuff, and I was wearing the helmet on a very windy day. I nearly took off a couple times, but the horns didn't break.