Originally Posted by
cyccommute
The tent in question adds 5 F compared to what? The open air or another tent? Even without knowing what the tent is compared to, 5 F is a huge temperature difference and just goes to show that the tent adds some value to the heat inside the tent.
No, it doesn't hold moisture to make you warmer. It doesn't blow heat away so quickly, basically not pummeling you with cold air. It's got nothing to do with adding moisture level to that air space. A tent is not meant to be a balloon in which you breathe into to hold the moisture in your breath. It doesn't work better that way.
I was referring to a bivy, not a tent. Even a bivy, directly over and sealed around a sleeping bag and pad only adds 5F in temp comfort range to the sleeping bag system when it is measured for clo-value. A tent would never be anywhere near that capable, no matter how buttoned up. A tent would be capable of steaming you out with dripping condensation though.