Ken wrote an answer about SealLine Baja Dry Bags on March 28, 2013
Hey Jen, this is definitely a bag I'd trust to protect my Macbook. It's a bit on the heavy side, but the durability gives peace of mind. I own the 30L which easily fits a 13" pro along with tons of other gear. If you're just looking to keep your Mac in it and no other gear, the 30L is probably way too big. I'd guess the 20L would still have a wide enough opening to fit the 13" pro in, but I can't say for sure. Hope this helps.