My Lexan Nalgeen's have never leaked, and they have taken some abuse for sure, including some rather impressive enounters with boulder fields that were at a significantly lower altitude than where I was climbing. Sometimes you are reaching back to clip the biner on the cap loop onto something on your pack, and miss, and then get to see just how strong Lexan is as it bounces down the mountain... It's also a test to see how good your memory is as you try to remember which area of rocks your bottle settled into so you can pick it up when you are on your way back down...