I completely wasn't thinking and it was early spring when I bought it, but I made the terrible mistake of buying a black bicycle helmet. I live on the 40th latitude with a large urban heat effect and I have long hair. There is a thin plastic shell on the helmet that can, no doubt be painted white without compromising the structure of the helmet and that alone should be big help (it's now deep dark glossy black). The helmet itself is glorified Styrofoam, or at least a relative of it because it is much harder. The Styrofoam is also dark, though it is a lighter shade of gray. Will it compromise the structural integrity of the helmet to paint the Styrofoam portion of the helmet?
As I said, I wasn't thinking and since my bike is black, I went with the black helmet. During the summer, the seat (which is also dark black) gets uncomfortably hot even after 10 minutes of being outside in the sun (like if I go in a store). This helmet, when it is sunny is killing me. Also, I got stuck in a rain storm and the thin plastic shell completely separated from the main structure of the helmet and so It's taped on, so removing it will be a breeze. Spray paint is nearly always oil based and I am worried that if I paint the main Styrofoam structure, it could weaken or melt the Styrofoam structure, which would mean I am wearing this geeky helmet for nothing. I've been biking since I was 8 years old and last spring was the first time I ever bought/used a helmet. There are times when I feel that conditions are safe enough and I take the thing off for a few blocks to cool down. I will mostly have till spring now to do whatever I am going to do (either splurge for a new helmet or paint this helmet).
One other thing.... How much of this inability to loose heat through your head just the helmet itself? How much of a difference would a white helmet make with a sun that's high in the sky? It appears to be well ventilated but it still leaving at least 70% of my head covered. IOW, how much would a lighter color (glossy white) help? Is it more trouble than it's worth?