Helmets not only protect you against head injury – they're also designed to minimize the shock to the rest of your body if you receive a blow to your head.
The slim design and minimal weight of modern climbing helmets make them easy to wear. For most climbers, helmets are standard equipment on aid climbs, multi-pitch routes, ice climbs, mountaineering routes, and anywhere rock and icefall are a threat.
Climbing helmets are made of high-tech plastics and polymers such as polycarbonate and high-density polyethylene. Some have a foam core with thin polycarbonate shells (similar in look to cycling helmets).
All climbing helmets will provide some protection against blows to the upper head. More traditional non-foam helmets are more durable and protect you best from falling objects. Modern foam-injected helmets protect you from front and side impacts.
A climbing helmet will work most effectively if it fits well. It should be snug enough to limit side-to-side and front-to-back movement. A well-fitting helmet won't dig into the back of your neck when you tilt your head back or impede your vision when you lean forward. Your helmet should be light enough to be comfortable and provide ventilation to keep you cool if you climb mostly in warm conditions. For alpine or ice climbing, make sure the size can be adjusted to accommodate wearing a hat.
All climbing helmets sold at MEC undergo rigorous testing to achieve a CE standard rating. The tests ensure that the helmet will limit impact forces on the head and cervical vertebrae when weights of standard sizes and shapes are dropped on it.
If they receive a hard blow, lightweight polystyrene foam climbing helmets should be replaced, even if the damage isn't obvious. The helmet's foam crushes to absorb impact, so even one impact will make it ineffective.
Even the finest helmet won't save you if it's in the trunk of a car or in your pack. Although no helmet can prevent all foreseeable head and neck injuries, it is best way to protect your grey matter when going for the redpoint.