Which is the lightest sleeping bag out there? There are many now that use the highest quality down and super-light nylon. The lightest ones come in at close to one pound. My own weighs just 19 ounces, and that includes the stuff sack - which I have left behind to save another 2 ounces. Even if you need a bag with synthetic fill for wetter climates, you can find some for around a pound and a half. If you really want to go light though, and you know the area where you’ll be backpacking well, you might try a lightweight bivy sack for both a shelter and sleeping bag. Just pile dead leaves or dry grass on top of it to create an insulating layer, and sleep in your clothes. I have done this with a seven-ounce bivy and stayed warm and dry on a rainy night.