With a whopping 37 wind windows, the 911 wins any 'Vents Top Trumps' games hands down.
The sheer number of vents means that each of them is rather small, though. Add a combination of an almost full coverage brow and scalp pad, and limited and shallow internal channelling, and it means cooling airflow is only average rather than astonishing.
The small peak is also fixed, so it doesn't shield your peepers as well as more adjustable or larger beaks. Multiple sizing ensures a close fit though, and the extensive padding is comfy as long as you're not a heavy sweater.
We had trouble with the dial-adjusted 'headband', which tightened fine but then refused to release, leaving us trapped in the lid. The problem got worse the more we rode it and we ended up accidentally snapping the cradle trying to escape. This should be covered by the warranty, but it wasn't very comfy even when it was working.
It's also one of the heaviest XC-styled helmets here, but it does come with a 50 per cent crash replacement offer.