Originally Posted by
4eyedbuzzard
An SOL bivy might work for a night or two. But, it's a vapor barrier, so it pretty much stops evaporative and convective heat losses. Because it blocks water vapor it will lead to condensation accumulating from your body's perspiration on and in whatever sleeping bag you are using. As you sleep, both heat and moisture from your body "travel" through the sleeping bag. It's a slow process. But as long as you are in the bag providing a heat source, most of that moisture will travel through and evaporate out of the bag. [Bags still retain some additional moisture but come to an equilibrium point with their environment and use.] If you put what amounts to a vapor barrier over the bag, you trap pretty much all moisture and it will condense. In February that will likely lead to either a wet bag or, if below freezing, ice forming on and possibly even inside your sleeping bag, and it will then provide even less warmth. It's very hard to dry out a wet and/or frozen sleeping bag in February (you need heat and airflow, aka a clothes dryer). If you're going to start in February, there's really no realistic way around a breathable 0 to 10 degree bag or system (like two bags or quilts). Keep it dry, and allow it to air out as soon as you get out of it (while it is still warm). Warm. Cheap. Light. Choose any two.