Before I started Lucky Sheep I did some research on the early evolution of sleeping bags. I found this amazing article from Field and Stream published in 1917 explaining the Eskimo version which used animal fur insulation and seal skin for fabric. Completely natural, breathable AND waterproof. I used these ideas to design the Lucky Sheep Sleeping Bag using wool batting and lightweight cotton or merino for the fabric. Make your screen bigger to read it. They talk about the nuances of different materials from way back before modern gear.