The problem is ultimately one of physics. All helmets work under the same principle. The force striking one’s head–acceleration mixed with mass–can’t actually be prevented. Physics says that energy has to go somewhere, right? What good helmets do is lengthen the duration of the impact itself (in the hundredths of a second range), reverberating energy through various structures and materials, to smooth a hit from a sharp, high-g strike to a relatively smooth curve of deceleration. Consider landing on a concrete floor or a pile of pillows. Which impact takes longer and which impact hurts more?