Unlined bottles are a no brainer. Sigg is left saying "Why didn't I think of that"? Can I buy stock in Klean Kanteen? I do suggest the poly top over the stainless. Mine has been dropped on many a rock, skipped across pavement, thrown by an angry wife, and used to fend off a seemingly rabid dog and still it holds water well. Water seems colder too and no plastic taste. Not sure if it is advised, but I use the dishwasher for these once a while and believe it or not stainless steal does not melt and warp in the hot water. Plus, based on the dog experience, for the ladies this would be much more effective in beating the lights out of a creepy dude in the woods! Very sturdy.