Material:ABS,PE,PP,HDPE Anti-shock Light weight,Good strength,Good toughness Petroleum, chemical, power ,construction, ... rib, two ribs and three ribs on the top of shell could be doneLock type of back hoop: Turning knob ... , Yellow, WhiteSize52-60CMFeatures· Safety helmet with a versatile new shell design of V rib with 6 cooling vents on top ... Helmet with 6 cooling vents on top of the shell