I made these bracers from craft foam to go with a dragon-inspired outfit. These are definitely for show only, not intended to survive real combat! That said, they do work really well for costume purposes as they're cheap, lightweight, and fairly easy to make.

Materials:

bracer pattern
3 mm thick craft foam (purchased at Michael's Jo-Ann's, etc.)
iron and press cloth (any thinnish cotton fabric will do)
stylus or some other utensil with a rounded point
hot glue gun
superglue
size #0 grommets and grommet setting tools
black elastic beading cord
matte ModPodge and brush

Step 1: Cut Out the Shapes From Craft Foam.

Using the pattern (download here), cut out the main bracer piece twice and six "scale" pieces from the craft foam. Keep in mind that only half of the bracer piece is shown on the pattern; you will need to trace another copy and tape it together to make the whole piece.

You may also want to check the length and width of the main piece if your arm is significantly buffer/longer than mine (I'm a 5'6" un-buff female).

Step 2: Use the Stylus to Score the Craft Foam Pieces.

Press just hard enough to make an indentation just inside the edges of all the pieces. I also scored the backs of the scale pieces down the middle to facilitate folding. Be careful to use an even amount of pressure or else you'll end up with weird divots if you tear the foam.

Step 3: Seal and Shape the Pieces Using an Iron.

I use my iron on the cotton setting (second highest heat) with a muslin press cloth in between and iron the pieces for about ten seconds, then fold or mold them to the appropriate shape. For the scales, this is just folded in half; for the main bracer piece I carefully wrap it around my forearm (wear a tight long-sleeved shirt if you don't have skin made of asbestos). The important part is to hold the piece in its intended shape until it cools down. I use a book to weigh the scales down while they cool, but you might need to have another person help you with the main piece.

The foam pieces are "sealed" when they take on a smooth, shiny look instead of the more textured matte look of the original foam.

Step 4: Glue the Scales to the Bracer.

There are markings on the pattern indicating where I put my scales, but you can play around with how you want yours positioned. Hot glue works well to glue the pieces on initially, then I use superglue to glue down the tips of the scales since I don't want a bunch of hot glue strings trailing off there.

Step 5: ModPodge the Bracers.

I use a fairly wide, flat brush to apply a couple of coats of matte ModPodge.

Step 6: Set the Grommets.

I placed the grommet bases along the intended channel and pressed them into the foam once they were spaced evenly so that I would know where to pound them in. There should be directions on the grommet setting kit explaining how to hammer them together, but I would recommend practicing on some scrap pieces of foam first.

Step 7: Lace Up the Bracers.

You could use a piece of black leather, ribbon, or really any long thin piece of material, but I opted for black elastic beading cord. With elastic lacing, it makes it possible to pull the bracer on and off without relacing the entire thing each time or having to tighten and loosen it.