Greetings. My 45F Mountain Hardwear sleeping bag is usually warm enough in summer months. However, I'd like to be prepared in case the temps unexpectedly drop to 32F, without carrying more weight than necessary of course.
My first thought is to get a Sea to Summit silk sleeping bag liner, which should add 10F of warmth but costs $69, and weighs 4.8 ounces.
My second thought is to get an SOL Emergency Bivy for $16, and weighs only 3.8 ounces, but I've been unable to find an advertised temperature rating. I know this piece of gear isn't really intended for multiple uses, but I'd be happy if it lasted for a week-long trip since it's inexpensive. I have heard that this can cause condensation though which doesn't seem right to me -- wouldn't that cause hypothermia and defeat the purpose of an emergency bivy?
Does anyone have advice on which path to take?