I've used it in the past and there is some condensation on the sleeping bag in the morning. Not too much though, and laying out both items in the sun in the morning for 1/2 hour in the sun is enough to dry them out. But it keeps you warmer than with sleeping bag alone. I've used it inside the sleeping bag as well to keep warm on cold nights so the sleeping bag is free of condensation but clothes get clammy. You can also use it inside the bag but not get into it, that way it breathes more and reflects body heat back to you, but it is much lighter to cary a space blanket for that purpose, especially one that has a thin plastic coating which makes it more durable. As an experiment I used both a Thermo-Lite Bivy and a space bag to camp out in 55F with only cold weather bike clothes (jersey, shorts, long bike pants and upper themals and wind jacket and pants). I stayed warm in 55F with Adventure Medical  Thermo-Lite Bivy and space bag, but I do not recommend it for more than one night since you have to dry things out.  The only allure of a Thermo-Lite Bivy is that it is cheap but it ends there. It is not breathable and it is not any lighter than the lightest waterproof/breathable bivies on the market.

 

adrian

--- On Sun, 1/18/09, Gary Blakley <gcblakley@...> wrote: