[dhgeyer]

Arai Quantum II (L): 3 lb 6.7 oz (Full Face Helmet)

Shoei RJ-AIR (S): 2 lb 12 oz (3/4 Helmet)

Even though one is a large and the other a small, they both fit me perfectly, which says something about the consistency of sizing among different makers.

Arai Vector (S): 3 lb 5 oz (daughter's FF Helmet).

HJC CL-15 (L): 3 lb 14.5 oz (My old FF Helmet).

I think, but I'm not sure, that there are lighter FF helmets than any of these out there, DOT and Snell approved, but they cost.

Very small differences in weight can make quite a difference in neck comfort over long rides, but much more important is getting the riding position right for you. If your neck isn't just where it wants to be, it'll hurt after a while. Arm position can have a big influence on how the nape of your neck feels also, so you have to get the handlebars right for you.