Wow, this thread reminds me of all the times I had to take my passport out of my neck pouch to change traveler's checks (in the days before ATM networks!). I would be standing in line on a hot summer day, with a huge backpack on the floor beside me, fumbling into my shirt (flashing the crowd, no doubt!) for a damp, bent passport. Those bank tellers would always look at it like it was a used tissue...ick!
But they do stand moisture pretty well, and I always just made sure I had copies in my bags (one in each) and with my parents at home.
I have a zippered leather travel belt (looks like a regular black leather belt, with the zipper on the inside), too, and keep an extra copy of the passport and some money (bigger bills) in that. It lies flat and nobody could get it off without my permission
!!
Tara