Iv been rocking the F5 Abyss Koroyd this year and really like it so far, im a little concerned how it will do on a below zero day because of its crazy ventilation. It has made for a perfect MX helmet this summer though. It is a couple oz heavier then my 509 Carbon.
I will just repost phattys review of it as he sums it up pretty well and it saves me some typing
"Klim F5 Helmet review:
Pros: lightweight, comfortable, fidlock, extremely well vented (like really well vented!), large goggle port, flat top for easy go pro mount.
Cons: fidlock, extremely well vented
Yes I know i have 2 items listed as pros and cons. I will get to those. First off the helmet is really light which eases strain on the neck and allows you to ride longer without fatigue. The helmet its self is very comfortable and fits my head well. The viewport is large and fits the oculus goggles well.
The helmet is so well vented that it can be borderline cold. This is awesome for slow moving, fighting in trees and creeks. This should help alot of people with fogging issues as the heat can get out of the helmet quickly. However, its so well vented that cruising down the trail at high speeds at 0 degrees is really cold, even with the goretex liner, this helmet moves some air through and cools you right down. This will be amazing in the summer.
The fidlock is both great and frustrating. Maybe I am just not used to it, but I cannot get the thing to lock with my thicker gloves on. I find myself having to take my thicker gloves off to get it to lock, which is annoying because I only wear thick gloves when its cold and i dont want to take them off. Maybe with some practice I will get better with it (i always used to buy the little clips that buckle in and out). I do love how easy it is to undo and with thin moto style gloves its super easy as well.
Overall I give the helmet 4/5 stars for winter, with the missing star because its super vented and cold on those early morning trail rides (even with headsock and goretex liner), but awesome in the trees later in the day.
For summer it will be an easy 5/5 for keeping one's head cool and not overheating. It is also light enough for use on my mtn bike.
Its a great step up from the F3-F4 IMO and I think many people will really enjoy this lid."