In reply to Sharp:
This should help Ben, there is a pdf guide to helmet types and uses on this page.
http://www.thebmc.co.uk/bmc-helmet-campaign
Foam helmets – soft in the head?
For quite a while, wearing a helmet marked you out as an arch-traditionalist. A helmet meant climbing VDiff’s in all weathers, drinking warm beer, and wearing Ron Hills to the pub. Cool climbers didn’t wear helmets, because they went sport climbing and bouldering instead.
That all changed when Neil Bentley climbed Britain’s first E10. You couldn’t get any cooler than this, and yet he was wearing a lid. And no ordinary helmet either, this was new, this was funky – this was foam!
Your typical foam helmet is made from expanded polystyrene (EPS) with a very thin polycarbonate shell. Compared to hardshells they are light and often very well ventilated, and it was these comfort factors as well as being new and fashionable which propelled them into a must have item for the aspiring wad.
In contrast to hardshell helmets, foam helmets provide protection even close to the rim. The thicker the foam is towards the rim, the greater the level of off-centre protection provided. This feature makes this type of helmet a good choice for the sorts of climbing where the main risk is banging your head in a fall. You can hit your head almost anywhere in a fall, whereas stone and ice fall mostly hits the top of the head (unless you look up!)
Impacts cause the cells in the foam to progressively collapse. The foam can crack into pieces, or even crumble completely with a large impact. For this reason foam helmets are not the best choice for longer routes and mountaineering where you can’t just pack up and go home. Damage during transport is also more likely than with other types of helmet.