Need One? Yes!!
The average careful bike rider may still crash about every 4,500 miles. Head injuries cause 75% of our 700 annual bicycle deaths. Medical research shows that bike helmets can prevent 85% of cyclists' head injuries. And helmets may be required by law in your area.
How Does a Helmet Work?
A helmet reduces the peak energy of a sharp impact. This requires a layer of stiff foam to cushion the blow. Most bicycle helmets do this with crushable expanded polystyrene (EPS), the white picnic cooler foam. EPS works well, but when crushed it does not recover. A similar foam called expanded polypropylene (EPP) does recover, but is much less common. Another foam called EPU (expanded polyurethane) has a uniform cell structure and crushes without rebound, but is heavier than EPS and its manufacturing process is not environmentally friendly. Other foams are beginning to appear that may offer promise. The spongy foam pads inside a helmet are for comfort and fit, not for impact protection
The helmet must stay on your head even when you hit more than once--usually a car first, and then the road, or perhaps several trees on a mountainside. So it needs a strong strap and buckle. The helmet should sit level on your head and cover as much as possible. Above all, with the strap fastened you should not be able to get the helmet off your head by any combination of pulling or twisting. If it comes off or slips enough to leave large areas of your head unprotected, adjust the straps again or try another helmet. Keep the strap comfortably snug when riding.
What Type do I Need?
Most bike helmets are made of EPS foam with a thin plastic shell. The shell helps the helmet skid easily on rough pavement to avoid jerking your neck. The shell also holds the foam together after the first impact. Some excellent helmets are made by molding foam in the shell rather than adding the shell later.
Beware of gimmicks. You want a smoothly rounded outer shell, with no sharp ribs or snag points. Excessive vents mean less foam contacting your head, which could concentrate force on one point. "Aero" helmets are not noticeably faster, and in a crash the "tail" could snag or knock the helmet aside. Skinny straps are less comfortable. Dark helmets are hard for motorists to see. Rigid visors can snag or shatter in a fall. Helmet standards do not address these problems--it's up to you!
A sticker inside the helmet tells what standard it meets. Helmets made for the U.S. must meet the US Consumer Product Safety Commission standard, so look for a CPSC sticker. ASTM's F1447 standard is identical. Snell's B-95 standard is tougher but seldom used.
Fit is not certified by any standard, so test that on your own head. Visors are not tested for shattering or snagging in a fall, so you are on your own there.
Coolness, ventilation, fit and sweat control are the most critical comfort needs. Air flow over the head determines coolness, and larger front vents provide better air flow. Most current helmets have adequate cooling for most riders. Sweat control can require a brow pad or separate sweatband. A snug fit with no pressure points ensures comfort and correct position on the head when you crash. Weight is not an issue with today's helmets.
Source: The Bicycle Helmet Safety Institute