Homemade Costume Tutorial: Transformers Optimus Prime

Sometime in September of 2014, Dallin decided that he wanted to be Optimus Prime for Halloween. I was, at first, relieved because he had not made a decision yet and I was getting antsy that he wouldn’t pick anything till the late minute. This relief was soon dispelled by a bit of stress as I realized that I had NO IDEA how to pull this off. CARDBOARD! Cardboard was the answer! Which was amazing for two reasons:

1.) We had just moved and had plenty of boxes around. (We were drowning in boxes, in fact.)
2.) My sewing machine had stopped working over a year ago and I still hadn’t gotten a new one. So a sewing-free costume was totally welcomed!

Even though these positives made my stress level go down a bit, I still procrastinated until the last minute to start the thing. It all seemed so complicated and with no detailed online tutorials to really help, I was just gonna have to wing it. So after some brainstorming and sloppy sketching, (and the day before Halloween with a nervous 6-year-old wondering if it would get done), I embarked on figuring out and building this intimidating costume.

Materials Needed:

  • Cardboard (lots of it and in big/wide sections)
  • Glue Gun and Glue sticks (lots!)
  • Duct tape
  • White Primer Spray Paint
  • Glossy Red Spray Paint
  • Blue Spray Paint
  • 1 White Poster Board
  • 1 sheet Yellow Craft Foam
  • 1 piece Light Blue Scrapbook Paper
  • Red cardstock (I just used the cover of an old notebook)
  • X-acto Knife or Utility Knife
  • Blue Gloves
  • Kid-sized Bike Helmet
  • Two Cardboard tubes (approx. 12″ each)
  • 4 Mini Shampoo bottles (or any other small cylindrical objects)
  • 2 Orange Juice Bottle caps (or any other short round cylinder type things)
  • About a 1/4 yard of 1/4″ foam

Step 1.) Taking Measurements


The first thing I had to do is take Dallin’s measurements. I measured his chest, waist and shoulder span as well as his arm length and diameter. I then measured his legs from ankle to knee and their diameter. I marked these measurements on a dummy sketch to keep everything straight.

Step 2.) Making the Torso’s Foundation Piece
For this step, I took one of the biggest boxes I could find (producing a cardboard piece at least 5 foot long). I took the chest span measurement and used that to dictate the width I would cut the piece. Then I let the cardboard go as long as it could without trimming… leaving a super long piece of cardboard. I found the middle of this piece and cut out a large circle for the head to go through. I used a Frisbee for this.

I made sure that the circle’s diameter wasn’t wider than the depth of the chest span. I folded over the cardboard to make two 90 degree folds at the front and back of the circle. I let Dallin try it on and trimmed the long front and back pieces (that were ridiculously long at this point) to about his waist. I wanted him to be able to bend over or sit with the completed costume on, so I wanted him to model the cardboard before cutting it to the proper length.

Step 3.) Strengthening your Foundation Piece with the “Cross-Grain Sandwich” Method
Up to this point, the cardboard was very floppy and not structurally sound at all. To remedy this, I took another super long piece of cardboard and made an identical piece of what I had just made making sure that the corrugated “grain” was going at 90 degrees this time. This was simple by just tracing the previous piece. No measuring needed this time.


What I did have to do this time was the score (not cut) the second piece, which had the corrugation going the long ways, so that it would fold neatly and precisely at the same place as the previous piece. I just made sure that I marked a line at the proper place (as directed by the previous piece) and lightly cut through just the first/top piece of paper of the cardboard.

I glued both these pieces together (with the scored piece on the outside) with plenty of hot glue. As the foundation piece, I made sure that the glue was sufficient to glue the entirety of the pieces together. I didn’t aim for 100% glue coverage but I did not dab glue just here or there. This produced a much sturdier foundation piece. (I had forgotten to cut out the circle opening for the head on the second one before glueing. I definitely recommend doing this beforehand.)

Step 4.) Adding the Sided to the Foundation Piece

To complete the foundation piece, I cut out two pieces of cardboard to fit the open sides. I used the measurements from the sandwiched foundation piece (the width of the opening and the length of the opening) and then drew that rectangle on a new piece of cardboard. I then used my trusty quilting ruler (I LOVE THAT THING!) to easily add a 1/2 inch “seam allowance” on the top and sides of the rectangle.

I then cut the rectangle with seam allowances still attached with a utility knife. Then I scored (not cut) the seam allowance folds. I cut out the corner notches for easier folding into a 3D shape. I then used these seam allowance sections to glue and attach the pieces to the foundation piece.

I glued only one side and the top seam allowance sections, attached to the foundation piece and then added glue to the third side and secured the final end of the foundation piece. This made the attaching process much easier.

Voila! This will leave you with a very boring looking 5-sided box, with the top side having a round opening and the bottom unenclosed and open.

(Note: In the picture below, you will notice the duct tape. This was because my original idea involved the back to be open-able instead of the torso being a “pull-over” version as it turned out to be in the end. This troubleshooting cost me alot of time but I was much happier with the end result. So duct tape at this step is unnecessary.)

 Step 5.) Adding the Breastplate to the TorsoNext, to give the torso the classic Optimus-look, I decided to add the breast-plated area. I had found a couple of nifty 90-degree pieces of chipboard in some packaging from an item I bought online a while back. I didn’t know what I would use them for but I decided to keep them. I thought they would make a good base for this 3D embellishment, as the area would need to be properly supported.

I realize most won’t have pieces of 90-degree chipboard (which is different than cardboard as it does not have corrugation but rather is just stacked and glued paper, commonly found as the back cover of construction paper books). I would have done a Cross-Grain cardboard sandwich if I hadn’t had the chipboard.

I cut each piece to the width of the foundation box and then cut a V-shape on one side (as pictured above). I then hot glued the whole non-V section to the foundation box (as pictured below).
I then glued an identical piece facing the opposite direction about 9 inches below the first piece (so the v-shaped side would be facing down instead of up). This would be the base to a rectangle piece glued on top to enclose the breastplate area (as pictured below).

To reinforce the area, I used duct tape to completely seal in the breastplate as shown below. At this point, I also decided to seal all the edges with duct tape including the head opening.

Step 6.) Cinching in the Waist

I could have just left the torso as is but it bothered me that, in pictures, it was clear that Optimus Prime had a very prominent inverted triangle figure going on. I had not planned for this up to this point and I hummed and hayed if I should try to fix it or not. After some debating with myself, I decided to go for it. It felt scary to do, as I did not want to ruin the torso I had made so far, but I thought if I could pull it off, it would be really worth it.

So I removed the duct tape edge under the breastplate area and made two score lines (see pic). I also cut through the seam allowance along the score lines so the section would bend easily. I also cut a section out of the front and back of the torso. Then I glued and taped the new shapes together.

Step 7.) Cutting the Arm Holes

This step is relatively easy. I just had Dallin slip on the torso and I approximated were the arms would go. I made sure not to make the holes too big. I also made the bottom of the holes round for comfort and the top squared off. I made the holes a little closer to the front of the torso than the back as well.

Step 8.) Duct Tape the Whole Torso

I started priming the torso at this point but the paint was not sticking to the cardboard very well. It was sticking to the duct tape pretty easily though. Also, the duct tape areas became glossy while the cardboard areas remained dull. So I decided to duct tape the entire thing, sealing in all the cardboard. This also made the whole torso much more durable.

I did my best to make the duct tape smooth and crease/bubble/defect-free. Though I wasn’t entirely successful at this, after the rest of the embellishments, it still looked pretty nice. I recommend cutting the duct tape with a sharp edge when dispensing instead of ripping by hand. This will give you a much cleaner edge. I ended up doing a second “coat” of tape in some areas to smooth it out a bit.

Step 9.) Making the Grill Abs

I measured from under the breastplate to the bottom of the waist to get the length of the area I have dubbed the “Grill Abs”. I used about a third of the width of the waist to determine the Grill Ab width. I then added two seam allowances (one for gluing and one to add depth). I cut out the piece of cardboard and scored the fold lines (as seen below). I also cut out the corner notches to ease the folding into a 3D shape.

I then glued the cardboard into a box shape using the seam allowance as I did in the previous steps. I used a quilting ruler to make a grid pattern on the front of the box. I quickly hatched out the areas with a pen that needed cutting out so I would not cut the wrong areas (as seen below left). I then used an x-acto knife to carefully cut 3 out of the 4 sides of each hatched out a rectangle and scored the 4th side (as seen in below right).  Finally, I pushed in the areas to give the “Abs” the grill effect.

Step 10.) Making the Forearms

I measured the diameter of Dallin’s arms and decided on the proper width and depth of the forearms. I also paid extra attention to the length of the forearms as I wanted Dallin to have a full range of motion, so I made sure not to make them too long.

I made an attached top with a circular opening and added seam allowances for glueing. I then cut out the shapes and glued them into the forearm boxes (see below).

Once Dallin tried these on, I realized they would slip off way too easily. To remedy this, I hot glued pieces of foam to the inside to cause friction and pressure which worked out great.

Lastly, to match the torso finish, I ducted tape the entire outside of each forearm (see below).

Stay tuned for Part Two where I tackle the helmet, legs and put everything all together!

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