There will be screeds of stuff arguing the toss but meanwhile I like this:-
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How good is your helmet? Will it actually protect your brain in your next crash?
These seem like easy questions, ones you probably think you can answer by reciting the lofty standards your helmet meets and the lofty price you might have paid for it. But the real answers, as you are about to see, are anything but easy.
There's a fundamental debate raging in the motorcycle helmet industry. In a fiberglass-reinforced, expanded-polystyrene nutshell, it's a debate about how strong and how stiff a helmet should be to provide the best possible protection.
Why the debate? Because if a helmet is too stiff it can be less able to prevent brain injury in the kinds of crashes you're most likely to have. And if it's too soft, it might not protect you in a violent, high-energy crash. What's just right? Well, that's why it's called a debate. If you knew what your head was going to hit and how hard, you could choose the perfect helmet for that crash. But crashes are accidents. So you have to guess.
To understand how a helmet protects—or doesn't protect—your brain, it helps to appreciate just how fragile that organ actually is. The consistency of the human brain is like warm Jello. It's so gooey that when pathologists remove a brain from a cadaver, they have to use a kind of cheesecloth hammock to hold it together as it comes out of the skull.
Your brain basically floats inside your skull, within a bath of cervical-spinal fluid and a protective cocoon called the dura. But when your skull stops suddenly—as it does when it hits something hard—the brain keeps going, as Sir Isaac Newton predicted. Then it has its own collision with the inside of the skull. If that collision is too severe, the brain can sustain any number of injuries, from shearing of the brain tissue to bleeding in the brain, or between the brain and the dura, or between the dura and the skull. And after your brain is injured, even more damage can occur. When the brain is bashed or injured internally, bleeding and inflammation make it swell. When your brain swells inside the skull, there's no place for that extra volume to go. So it presses harder against the inside of the skull and tries to squeeze through any opening, bulging out of your eye sockets and oozing down the base of the skull. As it squeezes, more damage is done to some very vital regions.
None of this is good.
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The article continues here
http://www.motorcyclistonline.com/gearbox/motorcycle_helmet_review/index.html and is well worth a read, it's very informative.
