I want to do the Dalish warrior armor from Dragon Age: Inquisition, but I don’t know how to make a pattern for foam pieces (such as the pauldrons) do you know how I could make them?
For armor made of foam, I find it easiest to make patterns and mockups out of cheap materials that act in similar ways – in this case, a thin cardboard would be a good option. It’s a bit stiffer than foam, but you can harvest it from cereal boxes for free and it’s close enough. Once you get the hang of it, make a mockup in cheap, thin EVA foam (like the craft foam sheets from a craft store) for a closer material match, and then move to a nicer foam for your finished product (or just stick with the cheap stuff! It works, but might need reinforcing).
For pauldrons, my biggest tip I can give you is to mind your curves. You know how you need to have seams in order to get a piece of fabric to create a curve? This is the same principle, only in foam. Something like this is going to be like sewing two curvier parts of a princess seam together. The seam at the parts you want to be rounder (like near the shoulder) will have a more pronounced curve, and at the parts you want less round (like near the arm) will have a less pronounced curve.
Experiment with creating curved seams in paper first, and then move your way up to nicer materials. Be sure to get the curve correct before you do any detailing or other shaping so that you can make sure that the detailing won’t change position too much if you need to change the curve. Any detailing that might need to cross any seams you have should also obviously be patterned after the seam curve is correct.
You can apply this principle to all sorts of shapes – need something with a more complex shape? Add more seams!
Once everything is shaped with seams, I would still recommend heating the foam with a heat gun so it can retain the curve easier and be easier to glue the pieces together.
Good luck! I hope that helps :]