I should add that the poster above is correct saying that more light coats is better than few full coats. I did 6 light coats each of paint and clear coat to get it to finish. It hold up great in heat, but the problem is that, when you are in cold weather and the paint gets cold, it shrinks at a different rate than the helmet does, so it is very prone to cracking and becomes very brittle. You could probably research more temperature resistant paint, but it will still be difficult to match the thermal properties of the helmet.
On another note, when you paint, don't forget to remove the shell from the styrofoam and just paint it separately, or make sure you cover up all the parts you don't want painted. I forgot to do that so now all my straps and earpieces have a whitish color to them, as well as being slightly stiffer and tackier. The chemicals in spray paint can also damage the styrofoam, making your helmet less useful than it could be in the event that you hit something hard. It won't compress correctly and your head will take more of the blow than it should be. Just my 2c.
