Messenger Bag Question

[0miss-sneezy0.livejournal.com]

I was planning on starting a messenger bag tomorrow, maybe something I can use for school. I was thinking about using pieces of an old towel to make it a bit thicker and maybe a little more "waterproof". Like I would use regular fabric, but just sandwich the towel in between it. I was thinking in case it rained, the towel would make it less likely for the water to soak all the way through to the stuff inside. So I was wondering , has anyone done this before? And does this even seem like a good idea, or am I way off base? :P And feedback would be much appreciated.