I have both the Nalgene Guyot in the 32oz and the Kleen Kanteen in I think the 22 oz, both wide mouth. While I've never had the need to boil water in either, both are rated by the manufacturer for that purpose in an emergency. There are you tube vids with the guyot bottle boiling water as I viewed one prior to purchasing my bottle. If a person was going to boil water in either bottle they had probably better have heavy leather gloves, a pot holder or pliers to handle getting it off the fire.

I like the design of the Guyot the better of the two, it just feels more substantial, I love the design of the cordage loop between the bottle and cap-perfect for hanging the bottle off of gear and the 32oz is just a better size for me as well as the correct size in the case of the need for treatment tabs.