>First, "it is impossible to build a cycle helmet that will offer significant impact protection" [1]. At this point I am not sure. The problem seems to be that

>First, "it is impossible to build a cycle helmet that will offer significant impact protection" [1]. At this point I am not sure. The problem seems to be that current designs are based on ancient studies of how much acceleration it takes to cause skull fracture. It turns out that it is extremely unlikely that you will get a skull fracture while riding a bike. The energy justisn't there. Hence, current bike helmets are pretty much useless for preventing brain injury. The energy absorbing foam is too stiff to crush in actual accidents so no energy is absorbed. Concussion on the other hand does happen a lot in bike accidents and is now known to be a fairly dangerous injury. That has caused a current idea that it might be worthwhile to design a helmet that works against the lower acceleration that causes concussion and doesn't work against skull fracture. Unfortunately such a helmet would not meet current safety standards and as a result could not be a commercial success.