Air tight and waterproof
I have owned 2 of the rolltop Seal Line bags for over 10 years with many days in a fishing boat or duck blind, and they have performed flawlessly. They are also tough as can be. No leaks, yet. I purchased the backpack to try for ease of use and to use while riding the bike to and from work. The makeup is the same as my rolltops, but have the convenience of straps. It has been waterproof and the straps can actually handle more than I would have believed. I have the 35L, though, and can see where the bigger the capacity gets, maybe the more uncomfortable the straps would become. I would recommend any Seal Line bag, because they have taken serious abuse from me. I think this Boundary Pack is going to become my "go to" waterproof bag, though. It is comfortable and a great bag.

Performed well; waterproof.
This bag holds a lot of gear. it was water-tight in rain. As a backpack, it is for occasional use; it works well for short distances. I would not want to carry it all day. I bought it for its weather protection and to have a convenient way to carry it short distances. It works great for this type of use.