With slightly larger lenses than the standard model, the Oakley Flak Jacket XLJ Transitions Sunglasses give you added protection as you cruise down the trail. These high tech shades feature Oakley Activated by Transitions photochromic technology. This means that the lenses lighten to show hazards in shaded areas, and darken to block bright sunshine. Throw in balanced light filtering and Oakley's High Definition Optics and you'll experience outstanding color contrast, clarity, and depth perception even in low light conditions. O Matter frames make the Flak Jacket XLJ Sunglasses feel incredibly lightweight, increase durability, and create balanced pressure points for a comfortable fit. When you work up a sweat, these Oakleys won't slip off your face Unobtainium nose pads and stem sleeves actually increase their grip with perspiration.