The Bike Helmet
The Consumer Product Safety Commission and the Snell Foundation certify helmets. Be sure the helmet says CPSC and/or Snell on the inside label. It’s often said that a helmet ages and should be replaced every three years even if you’ve never made love to the pavement. I don’t think there is much objective info on that one.
Fit is critical. Wearing a helmet on the back of your head like a beanie is absurd. Many bike accidents happen when people go forward over the handlebars. In that scenario a helmet sitting on the back of the head will protect about as well as a baseball cap. Strap positioning is also vital. The Snell Foundation has a good web site that describes how to fit a helmet. http://www.smf.org/helmfit.html.