Guyot designs (also sold under the Nalgene brand) and Kleen Kanteen are both un-lined steel bottles. You just have to make sure to stick to the single-walled variety if you want to boil water in them. They also sell insulated (double-wall) bottles, but these are not safe for boiling water over a fire.
Not safe? Or simply ineffective?
HJ
Im Pretty Sure not safe in the KABOOM kinda way.
Well, 'kaboom' is relative. Considering we're talking about a few cubic inches of dry air, this would be the equivalent of (consults conversion table) about 10,000 ant farts.