Hey PF, just a question out of my own curiosity that I've been wondering about. What type of equations/formulas/ and other things would I need to know to determine at what temperature breath [water vapour from our mouths/lungs] condenses in air ? I'm guessing something to do with specific heat values, partial pressure, humidity, and other things. Borek suggested Clausius–Clapeyron, but I have no idea how to apply it. What would it take for me to somehow "prove" the temperature/ humidity/ air pressure that is required for breath to turn into fog ? Thanks and discuss away.