Below is an excellent video by Yankee Self-Sufficiency comparing the “old school” goose down filled ECW military sleeping bag and the new issue ECW modular system. The video also shows you how to make a very inexpensive and very lightweight sleeping bag bivy out of Dupont Tyvek. For those of you that don’t know what a bivy is, it’s a lightweight waterproof shell that is designed to slip over a sleeping bag. Having a bivy will provide an additional 5 to 10 °C of insulation and will protect against wind and rain and protect your sleeping bag. So check out the video below and add a bivy to your sleeping system if you haven’t already.