Helmut is comfortable. I measure about a 7-1/2 hat size and the large size helmut works well. Fairly lightweight and stays in place during rides. Haven't crashed yet with this one on but my old Giro helmut absorbed a crash and being beaned by an errant golf drive :-) so anticipate this one will do the job as well.
It's light and comfortable. Great ventilation and easy to adjust. Trust the sizes-- I only know 2 people with heads bigger than mine. I measured my head and it was within the L range not XL as I expected. I thought there was a mistake, but since there wasn't an XL, I bought the large. It fits fine. If you have a king size cranium, buy this helmet-- it will fit.
As a long-time Giro helmet user, the Synthe MIPS II is the best I've used to date. Ultra-light, super-ventilated, and the added safety of MIPS II? What's not to like!
If you're too frugal - like me - to fork out the dough for the latest and greatest Giro helmet used by the PROs, this former PRO level lid is an incredible value.
This is my 3rd Giro Synthe; I bought it to save in case they are discontinued. This is the only helmet I will wear; it happens to fit my head well. It does not impinge on my neck. And it definitely saved me from potentially serious head injury when I wrecked recently. The helmet was totalled, but saved my head!