Edit: Link to PDF template.
The other day I decided that my three year old son needed a knight helmet for our foam sword fights, so I sketched a pattern on some poster-board, cut it out, and taped it together to make this:
He was loving the new helmet, and played with it a ton, but I figured I could do better. The next day, I took apart the poster-board helmet and used it to make a pattern out of printer paper.
I traced the new template onto some sheets of craft foam (the thicker ones that you can pick up from Michaels - 5mm I think). I cut out two copies of each of the long pieces pictured above, and one circle. I used contact cement to glue the edges together on these pieces. This stuff is great for foam because it gives a great hold immediately upon pushing the two pieces together. You have to spread the cement on each of the surfaces that will touch one another, and then wait around five minutes before pressing the pieces together. The 5mm foam is thick enough that you can apply the cement directly to the edges and it provides a large enough surface to hold together with the glue (which is important on the curves).
Once I had the basic helmet constructed, I drilled some holes on the right side for ventilation and because it looked cool. Then I sealed it with Plastidip (may have been Flexidip this time, but they are pretty much the same thing). The Pastidip/Flexidip is in an aerosol can like spray paint, but it essentially provides a thing rubber coating over the foam. This is important because the foam is very porous, and does not take paint well otherwise (it soaks it up). I also inserted some brads in various places so that they would look like rivets in the helmet (you can get the brads at a craft store like Michaels).
Once the sealant coat dried, I hit with some black primer. You can skip this if you use black Plastidip, but I only had red lying around. Once that dried, I gave it a few coats of a hammered steel spray paint ( I think it was Rustoleum). The hammered metallic paints give the foam a cool weathered texture and look less fake (in my opinion) than the standard metallic paints. After that, I painted some weathering on the edges and crevices with black acrylic and silver Run'N'Buff, and painted an X emblem on the left cheek (my son's name is Xander, so it seemed appropriate.
Here is the foam helmet next to the paper one. Not too bad for a one day build right? Xander seems to like it anyway...
Now I just need to make him a proper knight's sword and shield. I made the shield tonight, hopefully I can get the paint done tomorrow. I am debating whether to keep the X emblem on the shield, or do draw a dragon on there. We will see.
If anyone wants the templates I made, just leave a comment and I will post the pdfs. Keep in mind that they are made for a three year old, so you will have to scale up for a bigger kid or adult.