Top Gear #7 Petzl Meteor

The only disadvantage of this type of helmet is durability. A very lightweight shell covering a polystyrene dome means the Meteor is prone to damage if packed carelessly or, of course, if it is struck by an object. Infact, helmets of this type intentionally absorb impact partly by deforming and so they are more of a one hit design than some other types on the market. For this reason I don't personally wear this type of helmet for activities like ice climbing where being clunked by chunks of ice is fairly common. It also means that, should the helmet receive a significant impact, you should expect to retire it and invest in a new one. In truth I don't see this as a problem as replacing any helmet after it had taken a big impact is good practice.