The present invention provides a protective headgear having a multi-layered shell to sequentially extend time of collision of a blunt trauma to a human head and to differentially release an average impact force of the collision to the human head wearing the protective headgear across a mid layer of the multi-layered shell. The mid layer is configured to separate centripetal mechanical waves of the collision from centrifugal mechanical waves of the collision in phase with the centripetal mechanical waves so as to reduce summation of in-phase bidirectional mechanical waves of bidirectional mechanical forces upon the collision.