- First and foremost, the boats had to take the beating from sharp rocks and inevitably wrapping around those rocks. There is a big advantage to being able to deflate a boat if it gets wrapped (though I don't know if this is standard practice), since you can just peel it off like a wet blanket then. In addition, to my understanding it is easier to patch up a soft boat than a rigid one.
- We will be portaging, that means carrying everything over land. It definitely helps then to be able to deflate, roll up, and carry the boats on your bag like a pack. Imagine climbing mountains with a canoe - it's been done, but if we don't need to, we're not going to. This also means a smaller boat is better than a bigger one; so instead of choosing a full sized raft, we'll take the matchstick.
- Shallow water. With shallow water, the most buoyant boats help even if it's just millimeters. Inflatable means we maximize in that department.
All images by http://www.robfin.cz, pretty much the boats we hope for.