Cosplay Armor: How to Create Leg Armor with a Knee Guard

This tutorial will go over the basic technique for creating leg armor with a knee guard. Leg armor is fairly straightforward to make, so this is a great project to start with if it’s your first time using EVA foam. You can easily make a mockup with paper to make sure everything is right before cutting into your foam.

If you already have boots that look like leg armor, you can just skip to the part about the knee guards and learn how to make these and attach them to your boots instead. These are pretty similar to making pauldrons for your shoulders since you want to make sure your joint can easily move around with your armor on.

Supplies needed:

• Paper and pencil
• Paper towel or scrap fabric
• 4mm EVA foam (you can get away with 2mm foam if that’s what you have available)
• A sharp razor
• Contact cement
• Sandpaper or a rotary sanding tool (like a Dremel)
• Heatgun 
• Primer
• Flexible paint
• Elastic
• Brads (paper fasteners)

1. Create your leg armor pattern

The first thing you have to do when making any kind of cosplay armor is to make a pattern on paper. This way you can test out the size and shape of your armor pieces before you spend the time and money cutting into the EVA foam.

1. Measure the length and width of your leg and draw out a rough pattern. I’m making two separate pieces for the front and back of the leg armor that will be connected on the sides using elastic.
2. Cut out the armor pieces in paper and test them against your leg to make sure they look okay and feel okay. You want to make sure you have enough space around the ankle and knee to move freely.
3. For the knee guard, I first made a mock-up of the shape with aluminum foil. Simply squash foil together until you have the basic shape of your desired knee guard.
4. Using a piece of scrap fabric, paper towel, or newspaper (something more flexible than a standard piece of paper) cover the surface of the aluminum knee piece.
5. Pinch out a dart on both sides of the knee guard. This is the space that will need to be removed from the pattern piece in order to create the curved shape of the knee.
6. Trace around the rest of your knee guard shape and flatten the piece of fabric or paper. You’ll see that you have two shapes that are almost semi-circles. It’ll be a little messy, so clean up the lines and cut out the two halves separately.
7. Trace the knee guard onto regular paper and tape it together to make sure it looks right. The paper model should be curved.
8. Make sure the knee guard lines up with the top of the leg armor and make adjustments as necessary. This is why I included that top tab section on the leg armor.

Tip: when you test your knee pattern in paper add a couple of tick marks along the seam. This will help you align the pieces correctly when gluing them together later.

2. Cut out your pattern pieces

Now it’s time to take your paper pattern pieces and cut them out of EVA foam. I recommend using 4mm foam for this. 2mm EVA foam can work as well, but in general, the 4mm will give the armor more structure while also being easy to work with (thicker EVA foam is more difficult to cut, heat, and shape). Don’t forget to cut out a mirrored set of pieces for the armor on the other leg and transfer your tick marks onto the EVA foam.

As you cut, it’s a good idea to periodically sharpen your razor with a knife sharpener. EVA foam tends to cause blades to go blunt fairly quickly, so you’ll get more accurate cuts with less effort if you keep the blade sharp.

3. Glue the knee guard together

First, let’s set aside the leg armor pieces and work with just the knee guard. You will need contact cement for this part.

1. Apply the contact cement to both edges of the knee armor pieces. Wait 5 minutes for the adhesive to get a little tacky.
2. Starting at one end, start to press the two sides of the knee guard together. Try to line up your tick marks as you go.
3. The foam will start to bend around itself as you make your way from one end of the seam to the other. You can stretch and squish the foam as necessary to get everything lined up correctly.
4. Once everything is glued together, wait a few hours before sanding or applying heat.

At this point, you can also attach any 3-dimensional design attributes to your leg guards. If your character’s armor has a border, symbol, or other decorative elements, you can cut them out of the EVA foam and attach them now.

Tip: flipping the seam inside out can help to press the edges together, giving the contact cement a stronger hold. Turn it right-side out again after a few minutes.

4. Sand the armor pieces

Before moving on, it’s best to take the time to sand the edges and seams of your leg armor. This will help to hide any imperfections you made when cutting the EVA foam and will help you flatten the seam in the middle of the knee guard.

You can use regular sandpaper for this, but as someone who is impatient when sanding, I find it way quicker to use a Dremel. This is a rotary sanding tool that can quickly sand the edges of the foam. Just make sure to practice for a couple of minutes before using it on your armor pieces because it can take a minute to get used to.

Safety tip: When sanding EVA foam, always stay in a well-ventilated area, and wear a dust mask and goggles. You don’t want to breathe in the dust or get any into your eyes.

5. Heat-form your leg armor

Before putting the armor pieces together, we want to fine-tune the shape a little. The best way to do this is by using heat. When EVA foam is heated, it becomes more flexible. You can bend it into whatever shape you want, and the foam will remain in that shape when it cools down.

In this case, we want to create small curves in the front and back armor pieces, and we want to fine-tune the shape of the knee guard.

1. Heat up one foam piece at a time with a heatgun. Slowly wave the heatgun over the surface of the foam on the front and back. Avoid pointing it at one place for too long so you don’t risk burning the foam.
2. Then hold the armor piece curved over your leg until the foam cools. You may want to wear leggings or some kind of tight pants to protect your legs. The foam usually isn’t hot enough to burn skin, but it can feel unpleasantly hot.
3. When you let go of the foam, the piece should hold its new, curved shape. If you don’t like how it looks, you can reheat the foam piece and try again as many times as you want.
4. Pinch the edges of the knee pieces until they are the right shape for your cosplay. In my case, I’m flattening the bottom of the knee piece just a little bit.
5. Repeat the process with the rest of your EVA foam armor pieces.

Safety tip: EVA foam gives off mildly toxic fumes when heated. Always stay in a well-ventilated area when heat-forming your foam pieces and wear a face mask to keep yourself from inhaling the fumes. Once the foam has cooled it is no longer toxic. 

6. Prime and paint the armor

Now your leg guards are ready to be primed and painted. I recommend starting with a layer or two of a flexible primer. Cosflex and Flexbond are great for painting EVA foam because they are flexible paints that are not likely to chip and crack as the foam bends. This preps the surface of the EVA foam and makes the paint adhere there, rather than being absorbed into it.

After your primer has dried completely, use flexible acrylic paint to complete the look. Brands that I’ve used and liked are Liquitex and PlaidFX, but there are also many other brands coming out with flex paints that I haven’t had a chance to try yet.

• If you want to make the arm guards look metallic, check out my tips for faux metal paint
• If you want your arm bracers to have a leather-like look, check out my tutorial for faux leather paint

7. Connecting and wearing your leg armor pieces

Now all we have to do is connect the front and back pieces of the armor, then attach the knee guard.

1. Cut 4 pieces of elastic that will fit along the side of your legs. I used 1-inch thick elastic for this so that it looks more like straps holding the armor together.
2. Use hot glue (or your adhesive of choice) to glue the elastic to the inside of your armor pieces. Make sure the front and back are lined up correctly before gluing the elastic in place.
3. Poke 2 holes at the base of the knee guard through the upper tab of the leg armor. You want these holes to be right about where your knee starts to bend.
4. Insert brads (paper fasteners) into the holes and open the prongs to hold them in place. These will help the knee guard rotate slightly as you move your knee around.
5. Add a piece of elastic around the back of the knee guard. This will loop around the back of your knee to keep the armor in position as you walk around.

Try on your leg armor and walk around, making sure everything feels good to walk in. Test out some poses. Make sure you can bend down all the way, and test it on top of whatever costume you’ll be wearing underneath it to make sure everything is good to go.