The new Sirocco helmet from Petzl is moulded from expanded polypropylene EPP (as opposed to the more usual expanded polystyrene EPS) which has enabled them to create the helmet as a 'monobloc'. That is, it is formed as a single component rather than the usual layered structure of an EPS foam inner with a polycarbonate shell. It is superlight at 165g (for comparison the Petzl Meteor III weighs 235g and is one of the lightest helmets currently available). It also has a very nifty looking magnetic buckle - which they say you can clip with one hand. Here's a video from UKC at the Outdoor Show 2012: