I would recommend going up the helmet food chain far enough to get one with the plastic outer shell laminated to the styro foam material. There is no way for the shell to work loose that way, and if there is a "slide" type crash where the helmet is grinding along the ground, the outer shell cannot work loose (that is what the shiny outer shell is for - providing slip on asphalt in the event of the head sliding along the ground - preferably still attached to its body ;p)