Despite not being made of Kevlar, the Ballistic Nylon MK6 was often regarded as bulletproof. The MK6 is still rated at IP54, which means it can withstand water exposure up to a depth of 1 meter for 30 minutes. These are some common materials used in making motorcycle helmets: polycarbonate and ABS plastic are lightweight and shatter-resistant; steel or titanium is heavier but more durable; and leather is typically more protective than vinyl. All other things being equal, a helmet made of stronger material will be more protective. A helmet made of polycarbonate will protect you better from wood splinters and stone chips than one made of ABS plastic. A helmet made of steel will protect you better from road debris than one made of titanium. And a leather helmet will provide greater protection than a vinyl model. However, strength is not all that matters when choosing a motorcycle helmet. A helmet's internal design also plays an important role in its effectiveness. For example, a helmet with a large interior cavity is less effective at preventing skull fractures than one with a smaller cavity. Also, a helmet's adjustment system should be easy to use with either hand.