I've got a project to do for the kids. They want to put a Unicorn Horn
on their pony for a project. I looked all over google and ebay and
found that the horns that are sold are either cheap paper cones that
dont even look like a spiral horn and will fall apart, or costly ones
made of hard resin, wood, or plastic.

First off, we're not going to pay $50 or more for these things, and
secondly, I think the hard ones can be dangerous. Their pony is about
as gentle as you can find, but all it takes is one spin of his head and
some kid could get jabbed by the point.

So, the thought is to make one. Styrofoam can be gotten in cone shapes,
but I think it's too weak. We dont want it to break if the pony rubs it
on a tree or something, and would like to keep this for future events
too. That's when I came up with an idea. Take one of those paper new
years eve horns, and fill it with Great Stuff foam. After it hardens,
take silicone caulk and coat the outside of it with silicone, forming
the spirals with the silicone. This will create a soft horn that wont
hurt anyone.

The problem I see is that the silicone might just run down the cone and
not retain the spirals. Also, I wonder how long it will take for half
inch thick (in spots), to harden? The plan is to use white silicone,
because I know it cant be painted.

The thought did occur to put it on in thinner layers too.

Originally the thought was to make the whole thing out of Great Stuff
foam, but the way that stuff runs and expands, and makes a terrible
mess, I decided that was not a good idea.

Ideally, making it out of pourable latex, using a mold would be the best
way, but there dont seem to be molds for this, and I have no idea where
to buy the latex. Another thought was to wrap twine to form the thing,
and dip it in the latex, but I'm back to finding where to buy the latex.

I think the cheapest way would be the Great Stuff foam and silicone.
Under $10 for materials.

By the way, in case you're wondering how this gets attached to the pony,
it will get screwed onto the pony's leather bridle. I'll probably need
to stick a small piece of wood shoved into the foam at the base to hold
the screw.

Thanks in advance for all suggestions & ideas.