I am a professional motorcyclist so I can tell you this....
To understand how a helmet protects—or doesn't protect—your brain, it helps to appreciate just how fragile this all important organ actually is. The consistency of the human brain is like warm Jell-O. 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. Yummy!!!!!
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. 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. And NO this is not commonly referred to as having a “big head”! So anyway, it presses harder against the inside of the skull and tries to squeeze through any opening that it can. Such as bulging out of your eye sockets or oozing down the base of the skull. Even rupturing your eardrum and leaking out the side of your head. As it squeezes, more damage is done to some very vital regions.
We commonly refer to this as “NOT INDICITIVE TO A HEALTHY, HAPPY LIFE STYLE”
To prevent all that ugly stuff from happening, we wear helmets. The smart ones at least.
A motorcycle helmet has two major parts: the outer shell and the energy-absorbing inner liner. The inner lining is made of expanded polystyrene or EPS, the same stuff used in beer coolers, foam coffee cups, and packing material. Outer shells come in two basic types: a resin/fiber composite, such as fiberglass, carbon fiber and Kevlar (not the same Kevlar, or a molded thermoplastic such as ABS or polycarbonate, the same basic stuff used in face shields and F-16 canopies.
The shell is there for a number of reasons. First, it's supposed to protect against pointy things trying to penetrate the EPS—though that almost never happens in a real accident. Second, the shell protects against abrasion. Third, it gives manufacturers a nice, smooth surface to paint all those pretty pictures on. Riders—and helmet marketers—pay a lot of attention to the outer shell and its material. But the part of the helmet that absorbs most of the energy in a crash is actually the inner liner.
When the helmet hits the road or a curb, the outer shell stops instantly. Inside, your head keeps going until it collides with the liner. When this happens, the liner's job is to bring the head to a gentle stop—if you want your brain to keep working like it does now, that is.
The great thing about EPS is that as it crushes, it absorbs lots of energy at a predictable rate. It doesn't store energy and rebound like a spring, which would be a bad thing because your head would bounce back up, shaking your brain not just once, but twice. EPS actually absorbs the kinetic energy of your moving head, creating a very small amount of heat as the foam collapses.
The helmet's shell also absorbs energy as it flexes in the case of a polycarbonate helmet, or flexes, crushes and delaminates in the case of a fiberglass composite helmet.
To minimize the G-forces on your soft, gushy brain as it stops, you want to slow your head down over as great a distance as possible. So the perfect helmet would be huge, with 6 inches or more of soft, fluffy EPS cradling your precious head like a mint on a pillow.
Problem is, nobody wants a 2-foot-wide helmet, though it might come in handy if you were auditioning for a Jack in the Box commercial. So helmet designers have pared down the thickness of the foam, using denser, stiffer EPS to make up the difference. Of course this increases the G-loading on your brain in a crash.
PLEASE... Always wear a helmet when ridding a motorcycle. God only gave us one brain in a bucket so we gotta protect it!
