You know, I've always felt that the top shell to my Ultralite feels more durable than the material on the inside and bottom. Luckily however, I've never had a problem with the shell and in fact, it feels much more durable than my old Mountainsmith Wisp.

I just received my second bag, a Dakota SDL bag that was marked way down at moosejaw.com for whatever reason - it actually cost less than what I paid for my Ultralite 2 years ago. The SDL material feels pretty solid - like a lighter version of goretex paclite.