The helmet is about 2 feet-tall and is made of fiberglass-reinforced liquid plastic casting resin. For practical reasons the shop made the horns out of hollow plastic, but you should still feel their heft when you put the helmet on.
If you’re planning on cosplaying as the god of lies and mischief, you can also get the rest of his armor from Raptor with a Shotgun. That includes his armguards, a shoulder piece and a chest piece.
The shop even has a replica of the muzzle that they put on Loki in The Avengers.