For those few days when it gets hot here, I use the ripped t-shirt method under the helmet. Let it hang down like those French Foriegn Legion things. Now, if I were bound for a hot, sunny clime for an extended time, I wouldn't hesitate to get a British-East India pattern or French Colonial pith helmet. I suppose if you did a search you could come up with an old pic of French bike cop somewhere in old French Indo-China. Light as a feather and total sun protection. Crash protection? Bah! Hardly ever happens anyway. I'd be more worried about the heat.