Tact Bivvy Mylar sleeping bag by Survival Frog, Klymit 0 degree synthetic sleeping bag

When it comes to effectively preparing a 72 hour kit (otherwise known as a "bug out bag" if your evacuating) the ability to pack lightly to cover basic needs for survival makes all the difference. I wanted to know for myself 'how low can you go' in temperature while trying to sleep in a Tact Bivvy brand of Mylar sleeping bag, and how effective of an item is this for emergency prep and survival situations. I found the answer was about 20 degrees Fahrenheit as a low, while sleeping in it with my street cloths and a sweat jacket. However if I did it again I would probably try, as well as recommend, using two Mylar sleeping bags, one within another, for below freezing temperatures. I could have survived I think with just one but it did start feeling a little cold at least for my feet.