This looks promising. I just got a 15" rMBP and am looking for a sleeve that's as protective as possible, but also lightweight.If you're looking for a bulletproof sleeve that you can carry on its own or throw into a messenger bag check out chromes offerings. Great padding and doesn't add a lot of bulk.
http://www.chromeindustries.com/us/en/accessories/laptop-sleeves/tactical-laptop-sleeve
Do you have the Chrome one? Does it fit the rMBP tightly or is there a lot of extra space? According to the site, it looks like it isn't specific to MacBooks but just any 13/15 laptop. Also how much does it weigh the site doesn't say?