Hard hats, helmets and bump caps protect workers from impact and other workplace hazards. Bump caps protect against minor impact. They are made of high-density polyethylene (HDPE), which is lightweight and resistant to chemicals and moisture. Hard hats and helmets protect against heavy impact. Type I hard hats withstand vertical impact and penetration, while Type II hard hats have an EPS inner liner that withstands vertical impact, lateral impact and penetration. Hard hats and bump hats typically have vents to cool workers.