If you want something almost completely indestructible use the RITR Duracopy paper. That stuff is completely waterproof and has such high mechanical strength that you cannot tear it by hand. It can be printed on with a laser printer and most pens work on it also. The best pens for use on it are the RITR waterproof pens or running a very close second is an ordinary Sharpie marker or pen.
I've tested this stuff exhaustively for both caching and 'other' professional uses. It's fantastic stuff. The downside - cost is .65/sheet.
For most uses the ordinary RITR paper is sufficient. It can stand repeated wet/dry cycles and never loses it's mechanical strength, wet or dry. However, it does absorb water, but quickly dries out. It has about 2x the mechanical strength of ordinary paper, but maintains it wet or dry and its tensile strength doesn't deteriorate with repeated wet/dry cycles.
I'll update my earlier post about extended paper testing, hopefully later this evening for everyone's general info.
I've been trying to find paper that I can use for a cache that might get ALOT of water. I found a paper that it used for coupons and I actually did pretty well in my "water test".
Can you run Tyvek through a laser printer? It should be nearly indestructible.