Well, my last boomerang was just made out of foamboard that I painted and used some vinyl that looked like leather for the wrappings. It was really light weight, but the downside is that after one trip to Sakuracon, it was nearly falling apart from all the banging into peoples in crowds and the dealer room. Now I'm completely remaking it from scratch, but this time my dad and I went to a surfboard shop and got one of the foam blanks and are shaping that. We just finished shaping it, so now we're going to coat it in fiber glass so that it should withstand the beating it'll take easily. To get it the right color we're going to use the pigmented resin like they do for surfboards, so even if it gets dinged, it won't damage the color. Granted, my boomerang won't be a light as one made from styrofoam, but it'll still be relatively light, plus I wont have to remake another one every time I want to use the costume at a different con ^_^;;
