The how to details are a little sketchy, but the results of this DIY speak for themselves - it's a pretty slick looking laptop sleeve made from an old wetsuit.
Creator Alex says you can use any old neoprene wetsuit, as long as the piece of fabric which covers your back is big enough to fold over the laptop.
Because neoprene tends to be on the thick side, one thing you'd want to work out (which isn't covered in his post) is how fat a needle you need to use in your sewing machine (or maybe Alex should have asked his mum, since she did the sewing). :)
Neoprene Macbook Sleeve [Tinkerlog via MAKE]