Carbon’s Cosplay Corner : Insulation Foam

Hey Guys! Not too long ago, we talked about how to add magnets to large props, so this month we're going to talk about the insulation foam I used in the last tutorials. I know it's a little backwards, but I think it'll all work out well in the end.

Let's start off with a list of all the materials you'll need to work with Insulation Foam (IF), and a short list of its pros & cons. All materials have their strengths and weaknesses, and it's important to be able to recognize them so that you don't choose the wrong material for a project.


  • Insulation foam
  • Box Cutter
  • Replacement Blades or a Sharpener
  • Marker
  • Sand paper
  • Hot Wire Cutter (Optional)
  • Resin (or other liquid primer)


  • Light Weight
  • Easy to shape and Sand
  • Relatively cheap (5ftx8ft sheet for 20$)
  • Good for large projects and bulking out spaces
  • Sturdy when stacked


  • Easily dented and Damaged
  • Brittle when not stacked
  • Melted by Acetone, contact cement and aerosols.

IF is best for large & relatively flat projects, like bows, swords, flat shields and guns. As always, start with drafting your project out. Once you have the draft finished and sized to fit you, go ahead and transfer it onto the foam by tracing it with a marker. You can cut out the base shapes with either a hot wire cutter or box cutters. I personally prefer to use box cutters because I think they're safer, easier and cheaper to work with. After you cut out all of the pieces, it's very difficult to adjust the size of the prop, so be sure to double check the size after cutting out the first piece. While you're cutting everything out, I like to leave about 1cm around the edges so I can ensure that there aren't any gaps when the layers gets glued together. This is also when I add in any spaces for magnets or PVC pipes for easy disassembly. If you forget to do this part now, it will be a HUGE pain (if it's even possible) to go back in and carve out the spaces for the pipes and magnets. Below you can see some cut out and labeled parts for a bow I was working on.

Now that everything is cut out, I like to lay all the pieces on top of each other for a dry fit. During the dry fit, I'm checking to make sure there won't be any holes, or dips between the layers. To adhere the layers together, it's best to use a 2-part adhesive (JB Weld), but if it's a small and very light prop you can also use hot glue. If you're using hot glue, keep in mind that IF will slow down the cooling process for the glue, and frequently leaves small gaps between the layers. I used hot glue on the horn below, the gaps are hard to see now, but showed up very clearly after it was primed.

Once your adhesive has fully set, it's time to start carving out the shape of the final prop. While carving out and shaping the prop, remember to go slow, take breaks to save your patience and to replace your blades as soon as they start dulling. If the blade is dull, it will tear the surface, which is difficult to fix, but easy to avoid. Once the prop is shaped properly, go ahead and start sanding. Start with a rougher grit before moving to a smoother one. I normally only use 2 grits while sanding because I use a 3D print resin to coat the outside of the foam and it naturally wets out to cover imperfections like the ridges on 3D prints. Below are two horns, the right one is sanded while the left one has only been shaped. I decided I wanted a more natural look for these, so I only sanded these for about 5 minutes each.

After it's sanded down, I like to do a resin coating. The resin will protect the foam from being dented and prevent it from melting if you want to use a spray primer or filler. I normally use Epsilon Foam Resin for my large props, but XTC works just as well. I use almost the same process as in my casting article, but be sure to use a shallow pot or the resin will cure before you're able to brush it onto the prop. You can use other materials for protective layers (wood glue or paper mache), but they won't be as durable or protect the prop nearly as well.

Once the resin is cured, you can go ahead and fill and sand it down one final time if you'd like. Most of the time, I skip this step because I'm either in a bit of a rush or I plan to use any grit that's in the surface for texture or weathering. The resins themselves are fine to immediately start painting on, but I like to prime my projects with a gray primer filler to ensure that I have the same base color for all parts and pieces. It's a small, optional step, but I like to triple check to make sure that all of my paint will show up the same across the whole cosplay.

That's just about everything you need to know for working with IF! Next month, I'll being writing an intro on cosplay make-up! If you have any questions, be sure to leave a comment or contact me on Twitter! Until next time, get out there and make some mistakes!

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