What should I look for in a dry bag that will maintain its hydrostatic head (stay waterproof) forever?
I use a ~20L dry bag for a few reasons:
- To keep my electronics dry in my pack
- To wash my clothes
- To carry water from streams
So when I say "waterproof" I mean that it should both [a] keep water out and [b] keep water in.
I've owned a couple dry bags that were made of some thick nylon. Since nylon isn't waterproof, it's laminated with Polyurethane (PU). The problem with this is that after some years of abuse, eventually the PU delaminates and the dry bag doesn't hold water anymore.
This is curiously limited to dry bags: I've owned an MSR dromedary bag (which is a 1,000 denier nylon that's laminated with PU) for over a decade, and the PU has not delaminated. Why?
Are there any dry bags that are designed with 3-layers: a waterproof PU layer wedged between two nylon layers? Or is there some other dry bag material that's naturally waterproof and therefore doesn't require any waterproof lining that may fail in the future? What's different between the construction of a dromedary bag and a dry bag that makes dromedaries last forever while dry bags fail after a few years?