Piece of blue type II insulation. You can sand or carve it to shape first, and then put sandpaper on it. That, or quartering your paper, and folded not once, not twice, but thrice! What with all the curves, sometimes its easier to just do it by hand.
In my opinion. Plus I'm cheap and my compressor holds a whole gallon of air, which I don't think is enough for air tools.
