Step 2: The mold
If you note, the Predator's helmet has some complexity. It's not a closed helmet, and has features that difficult a two part mold. So, it will be requested a three parts mold.
Use the clay for making extra limits in the helmet. Look at the pictures for better reference. The limits function is to divide the helmet in three areas, everyone for a mold part. When the resin solidifies, the clay limits will allow to separate the mold parts.
You have to mix the resin with the catalyst and, if you want, some additive for thicken it. But be hurry, because once you mix the resin with the catalyst, you have a few minutes before it solidifies. You can find all of the components and indicationes in the specialized shop.
Cover the clay model with a layer of resin, foils of fiberglass and the again, at least three times. Don't forget the respiratory protection, the vapours of the resin are noxius. And use a lot of old newspapers and old clothes, because the resin will ruin everything it touches.