...and other misc materials :D One of the things that worbla is extremely good for is skinning a lighter and softer material to make it more durable, and this is especially good when you're wanting an organic shape for something like horns or antlers. I've made a few pairs in the past year or so, and thought I'd share the method I use. These are very lightweight and easy to wear, and the worbla makes them a bit more robust and able to take a few knocks.
I find organic shapes much easier to sculpt in soft materials - at least at first. EVA foam and insulation foam (available in large sheets from Bunnings) are both good options, and I've also heard of people using clay - though I haven't tried this myself.
Step one is to pattern out your horns for size and shape, and carve them to shape. If you're using EVA foam, a dremel or other rotary tool works really well, but you can also carve with a VERY sharp craft knife and sand them smooth. This takes longer, but if you don't have access to power tools, works almost as well. If you're using insulation foam, a sharp knife and sandpaper is all you need; a dremel will chew through the foam way too fast! Once the base shape is how you want it, you can start detailing.
Next up: cut a sheet of worbla a little bit bigger than your base shape, heat it up, and wrap it! Carefully trim away the excess plastic and smooth it out - heating it and then rolling it on a flat surface is a good way to smooth out any seams, but you can also trim and/or sand the seam once the worbla is cold. I like to trim it back and then smooth it out with Polyfilla.
When using EVA foam, I often have a hard time getting the base foam as smooth as I'd like it. Once I've covered the form in worbla, I use polyfilla to smooth out all the dings and get it nice and smooth.
BE CAREFUL: if you need to reheat the worbla when it's on your foam base, aim at the plastic only. If you blast the foam with a heat gun, it will melt away and leave you with a big hole! If this happens, don't panic. Although not ideal, you can fill the gap and sand it smooth again. It's harder to texture filler than soft thermoplastic, but it can be done. See below for an example - I tore a little hole in the worbla by mistake and the heat melted out a crater behind it. Polyfilla to the rescue! The right picture is the one I didn't melt, and was textured by pressing a knife into the warm plastic. On the polyfilla I had to carve a line out instead of just pressing it in, but it matches fairly well now that it's primed and painted.
As you can see above, both classic worbla and black worbla can be used with this method. I find that black isn't so good for a very highly textured shape, as it doesn't stretch quite as easily - but if you want a nice smooth base, then it is perfect.
Attaching the horns to your costume (or your head) can be done in several ways. Because horns made with this method are so light, you have a few options. Punching holes and threading them onto an elastic band is one idea, or glueing onto a piece of felt and sewing this into a wig; you can even screw them onto a piece of fabric or leather and use toupee clips to hold it into your hair or wig. Go nuts, and please show us what you've made! :D