Canvas is a great material that can be made more water resistant with wax for people who are trying to eliminate as much synthetics from their life as possible.  Part of a sleep system that included a wool sleeping bag that can be laced together.

Only a couple of samples in stock that came from a private collection.  Fully serviceable and in great condition for being ancient.  That said, you can probably hunt for a better deal online where they have these available in bulk.