I have two kinds, polypropylene (PP) and polycarbonate (PC/Lexan). The PC ones are wonderful -- strong and clear -- and don't impart a stale taste to the water like the PP ones. However don't try to remove the price tag from a PC one with an organic solvent like GunkOff or paint thinner -- it will dissolve the plastic. PP seems to be OK with solvents.

SnowPeak makes titanium 2-piece (around $30) and 3-piece (around $50) cook sets that fit a Nalgene bottle. This includes a pot, a lid, and for the 3-piece, a cup. I plan to get that (or the cheaper stainless steel one from Campmor) soon. There have been a couple threads about carrying a container suitable for boiling water, and that would beat an improvised aluminum foil container any day.

That would go in my knapsack for day-hikes. I have been giving some thought to being prepared for a day hike that turns into an unexpected over-nighter. Perhaps a subject for another thread...

Lots more info is at http://www.nalgene-outdoor.com/technical/

Steve
_________________________
"After I had solaced my mind with the comfortable part of my condition, I
began to look round me, to see what kind of place I was in, and what was
next to be done"