Cheaper method for the use of Worbla
If you are already working with Worbla, or if you are considering using it in upcoming projects, you're most likely familiar with the "sandwich method". This is when you cut your main armour shape out of craft foam and cover it in both sides with Worbla. I found this to be extremely wasteful since you use twice the amount of expensive thermoplastic for each piece of your armour, and when it's a huge project you end up spending an insane amount of money just for Worbla.
I found it more convenient to just cover one side of the foam piece and fold the excess thermoplastic on the back. This also makes the piece less rigid, and when you need to reheat it in order to shape it onto your body, it requires much less effort, it burns less, and it doesn't form air bubbles between the foam and the thermoplastic. I also found it easier to just decorate the foam piece before covering it with Worbla, which again, is cost effective since you don't have to use more of the thermoplastic for decorations.
Just build your armour piece with the decoration pattern on it, heat up your Worbla piece and put it on top of the foam. (in this tutorial I'm using a 5mm foam for the body and 2mm foam for the decoration). It is important to have a variety of sculpting tools, even the cheapest ones you can get, in order to shape out the pattern.
Just keep heating the Worbla for 5 seconds and press on with the sculpting tools until you reveal the pattern.
After you're done with the front of the piece, turn it around and cut away the corners and edges. Heat it up for a few seconds and fold it.
Don't worry if the corners don't align properly or if you cut more/less of the Worbla. Heat it up, pinch it with your fingers and while it's still mouldable cut it with scissors and the corner will look flawless.
After you're done with the folding, while it's still warm, heat it up a bit and shape it onto your body.
Here's a little tip: for the screws and rivets of an armour piece, just use Worbla scraps. Even if it doesn't show up, after painting and weathering, it'll look good.
If your piece has curves, do small cuts on the folding area of Worbla, but not all the way to the foam. You just need to be able to fold it behind the foam without the thermoplastic stretching or folding onto itself, thus creating ugly tears or creases. This step is very important if your armour piece doesn't have straight edges.
And this is how you craft big or small projects without using double the amount of Worbla for each foam piece.