Executive summary = amazingly light, surprisingly good fit, downright embarrassing appearance.
Details, drawbacks first:
1. Sizing seems too big for the spec. My head circumference is 57.2cm, which over the years has matched up well with my ski helmets, bike helmets, the CAMP Speed "1.0" 56-62cm range, and other climbing helmets. The Sirocco Size 2 is 53-61, and front<>back was okay, but the sides were just sticking out far too much. I was able to get the Size 1 48-56cm to work by removing the small comfort foam piece in front.
2. Appearance is so bad that it's good, like a really good bad movie (or when Orwell decided that Kipling was not a bad good poet, but rather a good bad poet). Something about the contours, the color, and the texture all taken together is just so very wrong. Either Petzl designers are so good that they care only about function, or instead if they care about styling then they are utterly incompetent. So try to take your pictures such that the top of the helmet can be cropped out (seriously), like in the attached photo.
3. The straps are so narrow that they're easy to twist up when putting on the helmet. But they're so thin that even when twisted they're still super comfy.
4. The magnet to enhance one-handed connection of the chin strap is clever, but it can allow the strap to be closed insecurely with only one of the two side clips engaged. Once aware of this possibility though, it's not longer a problem -- just need to remember to check that both sides of the clips are engaged.
5. Compared to the CAMP Speed, seems to have slightly less side protection. Although if that is an important issue for you, should get a dual-cert ski/climb helmet.
6. Vents are impressively ample. But realistically no climbing helmet will ever vent well at ascent speeds, since it has to be solid up on top to be certified. Does cool down very well on skiing descents at speed, so well that when I tried it in a race with nothing underneath on what I thought was a warm day I got the worst "ice cream headache"!
And now the pros:
1. Weight. Yes, that can be summed up adequately in a single number, but it's still amazing.
2. Durability. As demonstrated to me by a Petzl rep, you can step on this helmet, smush it, etc., w/o worrying about damage to the thin plastic exterior ... because there is no thin plastic exterior, just a single piece of foam. So it's been my favorite now going into its fifth season when strapping a helmet to the back of my pack for long dry approaches in late spring and summer when it might get jostled around back there.
3. Can also attach a Petzl Vizion visor, but my impression is that those are more for ice climbers, so I've stayed with the usual assortment of sunglasses, wrap-around shields, and ski goggles.
4. Strap system is brilliant. With just thin straps, Petzl has achieved the same adjustable and snug front<>back fit that is usually achieved by much more bulky adjustment systems/knobs/etc. at the back of the head. In addition to weight savings, less interference with wearing a sun cap underneath or sunglasses retainer.
5. Headlamp clip in back is minimalistic (well, of course, everything has to be at this weight) yet effective, and even securely holds a wide ski goggle strap.
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