Every year since college, Heather and I run the Living History Farms Race with friends. Being the costume-loving fools we are, we always dress up and have a theme. This year, our theme was ‘Under the Sea’. We’re trying to be a little cost-conscious, so we decided to make one costume for both Halloween and the LHF race. I was looking for something fun to build that would let me experiment with a new prop-making material: pink insulation foam. I decided to go with a treasure chest.

Build process:

I started off sketching. You can see some of my process shots below:

Treasure-Notes

Once I had a basic idea for construction down, I was off to Menards1 to grab supplies. Wandering around the aisles, I found a Rubbermaid tote for a few bucks. My original plan called for just framing up the foamboard, but I figured having an inner shell to attach things to would help the whole thing stay together. I had to borrow my father-in-law’s truck to get the foamboard, since it only comes in 4’x8′ sheets and I didn’t want to break it down before knowing my final dimensions. I went with a 1.5″ sheet, and it was about $18. Not bad! I picked up some coins and jewels from Hobby Lobby for just a few bucks and grabbed some large cardboard I had laying around.

Always make sure to use proper PPE when working with dangerous materials. Fumes and particulate dust are no fun to breathe. I also used eyeglass shields when cutting/grinding things, which can save your eye! Wear them.
Treasure-01

I started by cutting off the bottom of the container with my trusty Dremel.
Treasure-02

I measured and cut the foamboard on a table saw,2 then glued them together with Liquid Nails.
Treasure-03

All framed up and clamped together.3
Treasure-04

I forgot to take a few pictures here, but once the frame set up, I used a can of expanding gap foam to fill the gap between the storage tote and the foamboard walls. It’s the yellow stuff in the below picture. It is super sticky and dries rigidly, so it’s great for basic filling like this. I also laid down a few coasts of Kilz latex primer.4 After that dried, I picked a shaped grinding tip for my Dremel and started carving out woodgrain lines and board gaps. I went too light on the first side and eventually found a depth that worked for me.
Treasure-05

Next I started on the lid. I was worried about so much weight being cantilevered out away from my body, so I went with cardboard. It’s great for value, and can be fairly rigid provided you take note of the corrugation. I based my measurement on the width of the box, then roughed out an arc. I cut out half, then folded it over on itself for symmetry.
Treasure-06

I traced its mate out, then cut a long piece of cardboard the width of the box. I was too lazy to use math to figure out the proper total length of the lid piece, so I just cut extra and trimmed the excess. I also made sure to cut it out so that I could use the corrugation grain to my advantage when bending it around the arc. I used Gorilla tape every few inches to secure the lid.
Treasure-07

When I was almost done with the lid, I realized I hadn’t figured out the hinge situation. I improvised by leaving a few long flaps that got some Liquid Nails to secure it to the base. I was impatient and thought this would be fine, and indeed, it was serviceable. I also put down a first coat of brown. I found a few spots I didn’t completely seal with latex after this (had some pitting, whoops), but the new paint layers sealed those gaps just fine. It didn’t bother my aesthetic since these were supposed to be old, but keep it in mind for other projects!
Treasure-08

I couldn’t figure out how to make my elastic skirt concept work in my head, so I went with my backup plan. I cut out a shelf/liner thing out of cardboard and wedged it in around the inner lip, then ran Liquid Nails around it to bond it.
Treasure-09

While this was drying, I drilled out holes for the shoulder ropes and tied them off. After the next step, I wouldn’t have access to the plastic here any more.
Treasure-10

Again, I skipped a few pictures since I was working so quickly. I went through another can of expanding foam to fill the shelf between the top edge and the skirt edge. Since the stuff is so damn sticky,5 it would hold everything in place by itself. I sprinkled my first bag of plastic coins onto the top and let it set up. After it dried, I used a serrated steak knife to saw away the excess and straighten up the walls.
Treasure-12

I also sprayed the inside of the lid matte black, then dusted over it with brown. To get the plank look6 I used more Gorilla tape in parallel lines with a small gap. Then I just trimmed the excess off with my X-Acto. Once spray painted, it looked great!
Treasure-11

Dry test fit of the lid. You can see I’ve started weathering the chest. I used dry-brushing techniques, and also used a rag to wipe off excess. It’s a little black, but will smooth out with another light coat of brown over it.
Treasure-13

Couldn’t resist getting into the costume to check the fit! You can also see I’ve given the coins/foam inside a first pass with gold spray paint.
Treasure-14

Tight fit, but it’s what I was going for. Maybe I should’ve rounded the corners to eliminate the gap but I was almost out of time.
Treasure-15

I knotted the rope with a simple overhand knot to help maintain tension on the line while keeping the handle look.
Treasure-16

I used a few knots to secure the lid rope to the shoulder harness. It was difficult gauging the right amount of tension/slack to leave in the line, but I eventually arrived at a decent enough solution.
Treasure-17

I almost forgot the best feature!! A cupholder for my beverage. I used my trusty Dremel and serrated knife to carve back out a spot for a frosty one. I lined it with more Gorilla tape and sprayed on more gold to match the rest of the loot.
Treasure-18

I hit the lid’s ends with a coat or two of flat grey over the Gorilla tape, which worked pretty well. It almost ran in a few spots since the tape wasn’t roughed up beforehand, but I just eased back on the paint volume and it ended up okay. It’s getting there!
Treasure-19

Final details. You can barely see it, but I added more layers of coin to help cover the seam between the foam and the foamboard. I cut the lock out of some thin craft foam. Just eyeballed the shape, and used my “draw half, fold over” method from earlier to get a balanced piece. Then I backed it with another black piece of foam for depth.
Treasure-20

Just needs a little more weathering on top to balance it out. You can see the marks from the clamps that I neglected to smooth out, but it was less noticeable in person.
Treasure-21

Aaaand done. I wasn’t worried as much about matching the top and bottom precisely, since I would mostly be wearing it, but I ended up getting pretty close! The dry-brushing really helped the piece look aged. I even ran a paint marker down each of the lid side plank gaps and followed with a rag to get a subtle shadow effect.
Treasure-22

Success! I paired my treasure chest with a simple pirate costume.
Treasure-final

LESSONS LEARNED:
  • I should have planned out my hinge better. After just a few hours of total wear, the simple cardboard hinges started sagging, and my rope handle lid rig failed, causing the lid to flop all the way open. Getting actual hinges and drilling through to the plastic tub to bolt it through would’ve prevented that.
  • The lid itself should have been more reinforced. There is some play where the top meets the sides and the tape has shifted. If I was doing this again, I would’ve fiberglassed over the whole thing. That’d also help the hinges I mentioned have something solid to move against.
  • I also should have given myself more time. I was up agains the clock and had to cut corners to finish on time. Just like with a few previous Halloween costumes, the spray fumes were obnoxious to deal with while wearing the costume. If I had another week to air out the piece, it wouldn’t have been an issue.
  • I really need to evaluate whether a bulky oversized costume is the right call. This was my first event with something big like this, and it made getting around the house party fairly difficult. I can’t imagine a packed bar or convention hall!
  • Since this was my first time working with pink insulation foamboard, I wasn’t totally prepared for how easily it chips. I didn’t reinforce any of the corners, and over the course of the two events I wore it to, it suffered some chips from doorways and counters. You can see on the final costume picture a few spots that were already flaking away. I would fiberglass the corners next time.
Final Thoughts

With approximately 13-16 hours of total build and finishing time, over a week, this was pretty quick. Nevertheless, I had a lot of fun making it, and can’t wait to try making more stuff with the pink insulation foam. It carved well, was light yet durable7, and was pretty cheap. It also gave me a lot more confidence in my ability to make things up on the fly. Not sure that is a good thing, but it also means I’m less likely to stress about totally ruining a piece and more likely to take fun chances.


  1. like a Lowes or Home Depot 

  2. foamboard is almost too light to get through the saw…at the 4×8 sheet size, I had some issues pushing it through all the way by myself. I should have probably gotten a second pair of hands. Even had one of the planks kick back – even something light like that packs a wallop getting shot back at you by the table saw! 

  3. Future lesson: getting the clamps tight enough left marks in the foamboard that were hard to get out. 

  4. You have to seal the foamboard if you’re going to use sprays, as the propellant will eat away at the untreated foam! 

  5. seriously, don’t get it on your hands. It’s worse to deal with than super glue 

  6. and to hide the initial tape from rolling the lid 

  7. in the sense that it wasn’t flimsy. It chips pretty easily. I will try using a resin to get a harder surface for future builds