The z1 fast helmet has an integrated and non removable cover that is attached to the eps liner to create some serious advantage the z1 fast has a distinct advantage over a regular road helmets aerodynamic performance the shell closes off most ventilation holes thus it creates a surface that glides through the air much easier it does however keep the rear vents open to allow heat to exit the helmet tests have proven that the z1 fast helmet can provide gains between 4 and 10 watt when cycli