The Perimeter Seal system is the latest technology from Racing Optics which allows for a tighter seal to the visor, blocking out dirt, dust, and water from behind the tearoff stack. The laminated technology creates a distortion-free optical lens. The XStack is a stack of 10 laminated tearoffs that are 2mm thick each. Each package contains 3 stacks of 10 tearoffs for a total of 30 tearoffs. Compatible with the M8 Carbon, M8, Dominator2, K1 Pro, and GP2 Youth.