Question on how to use insulation foam for props?

I've always wanted to make the dragon slayer sword from the anime Berserk, and so finally I decided I was going to step out of my comfort zone of small and medium sized props and make this behemoth. So i decided of all possible option that the pink insulation foam would work best(if you have any other suggestions please let me know) , because I found that due to its size the foam would be the lightest. Now this is just going to be a show piece I'm not taking it to a convention or anything like that, but my problem is that I've never used this type of foam before. So I looked online and boy was there a multitude of ways on how to work with stuff but no real clear cut answer. I found that a lot of the sites gave me information but not really any real clear information on how to use the stuff. So my question to you guys is how in the world do i work with this stuff i know that spray paint will just eat it away so I have to give it a protective coat. Which some people use mod podge, Elmers wood glue, Elmers white glue and Gesso to do. As well as is it ok to paint(most likely using either spray paints and model masters enamel and acrylic paints for details) right after applying these things or do i need to do something else as well to it or is that it?

It really is as easy as it seems, or rather it is easier than you think it should be. Cut it with basic tools or use a hotwire cutter. Sand it down to finish and use acrylic paint to coat it. If you don't have an airbrush just brush it on with a chip brush or foam brush. If it's big enough object then investing in one of the air brushes from Harbor Freight might be worth it.

Gesso is used for prepping canvases and other surfaces for painting but I'm not sure it's really cost effective in this use. It's basically just acrylic paint with a fine grade powder added as a filler to make it sandable.

If the job is going to be big enough I would suggest considering using household latex paint to coat it. It's the solvents in most spray can paints that melt the EPS foam so using an air brush or just a brush with an acrylic base will be fine. You'll probably wanna thin the paint a bit with water if you use an airbrush.

There are foam safe spray paints out there, but they are made by companies catering to the foam airplane builders and so the cost is higher than the gesso and I haven't seen much in the way of color selection from them. Though it might be acceptable if you just want to use it as a protective coating for other paint.

Awesome thank you i do have a couple of airbrushes i have the both a harbor freight one and an Iwata Neo. I think though if its just the solvent than ill just buy some acrylics and paint it. Now kind of a dumb question here if i paint over it with the acrylics i can do a couple of layers of paint correct or is it a one and done deal, and can i also just use regular bondo if i accidental make a mark in it or must i use a specific filler?

my technique is an electric turkey carving knife to trim the foam to shape and after im done with that I spray 3-4 layers of plastidip, then enamel spraypaint over that when im done

To cut really precise and clean shapes i used a scroll saw with a homemade tooth-less blade (I just dremeled off the teeth) it works just perfectly, cleaner cut than a hot wire cutter and no melting problems.

Use as many layers as you would like of acrylic paint It won't matter. However my experience with Plasti Dip is that once the rubber has dried it continues dissolving away the EPS foam underneath, resulting in a cratering effect to the foam. Great if you'are wanting a pumice rock look...not so much for anything else. Bondo? On EPS? I've not tried it personally but I understand that it too will melt the EPS foam.

Once you have a layer of paint it might be fine although I would wonder about adhesion of the bondo to the paint layer.

Another good tool for shaping in wire brushes (hand held) you can shape up the big parts with minimal effort

but for making a sword to get the smoothest shapes you will want a foam hot wire cutter.

Ok so i think then I'll probably go with just the acrylic paints, and yea i ended up buying a hand held hot wire cutter as well as building my own bigger version. So then another question, if i paint on a base of acrylic paint then can i take my airbrush and spray some enamels for detail work? Thank you for all the help i really wouldn't have been able to figure all this out without your guy's help.

Assuming you let the acrylic paint dry, and have good coverage I'm sure it will be fine.

Ok great thank you so much for all the help. Now its time to get started on this thing.