The MacBook Air weighs a little over 1.3kg. Airy, but there's lighter. Not surprisingly, Apple wants to weigh that little—under 1.3kg. The easiest way to cut the fat is to use a material less heavy than aluminium that won't compromise the body's integrity. Enter carbon fibre, which AppleInsider says might replace the Air's lower aluminium case.
AppleInsider says a pre-production MacBook Air running around looked exactly the same as the current model, but with a black carbon fibre bottom. According to the teardown geeks at iFixit, the heaviest structural component besides the unibody chassis—which supposedly will continue to be machined from a single block of aluminum—is the bottom cover. Replacing it with carbon fibre would bring the Air's weight down by 100 grams to 1.26kg, lighter than the Samsung X360, and that's without shaving slivers of weight off elsewhere in the Air's design.
AppleInsider reiterates that they're publishing the info on the carbon fibre redesign "strictly as a rumour," but adds that it's far enough along in the dev cycle to show up in a MacBook Air revision next year. It sounds plenty plausible to us, though maybe not with that mismatched black bottom. [AppleInsider]