There is more to a sleeve than meets the eye. The 4mm walls are for optimal protection and minimum weight. This sleeve also has a specially designed gusset and mesh interior to let your laptop breath. Ever think about putting your hot laptop in an insulated sleeve? Now your laptop will cool down that much faster. The neogreene is waterproof, too, so if you spill on the outside, no problem. Easy to grab zipper pulls (2, by the way) round out the thoughtfulness. This is no ordinary sleeve.