I carry one 2.5-liter platypus (for camp use), one 12-oz salad dressing bottle and 1 quart used vinager bottle. Since I regularly buy salad dressing and vinager each is essentially "new" each trip. (The used bottles actually will deform if you try to add boiling water so do not use these if you ever intend to put in boiling water.) The salad dressing bottle is more flat and has a fairly wide mouth so it fits in my side pockets very well and is easy to add drink mix. I only carry the 12-oz bottle full of water when traveling. I usually have good water sources all along the trail. Rather than problems with heat, my bottles often freeze. The only problem then is that I get to carry ice around until it melts! I only use the tougher Nalgene bottles when I know I am going to bang them around a lot (like on a rock climb). The platypus and Nalgene bottles will tolerate boiling water- I rinse out each with boiling water after each trip and store them with caps off. (otherwise I often get algae in the bottles)