According to http://www.bhsi.org/guide.htm http://www.bhsi.org/guide.htm : "Most bike helmets are made of EPS foam with a thin plastic shell. The shell helps t

According to http://www.bhsi.org/guide.htm http://www.bhsi.org/guide.htm : "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.... Beware of gimmicks. You want a smoothly rounded outer shell, with no sharp ribs or snag points." I don't think a hat over a helmet is going to skid as easily as slick plastic. Also, "Dark helmets are hard for motorists to see," and this helmet looks like it only comes in black.