Made from the common weed known as stinging nettle, and as you probably know, as a weed, stinging nettle is very durable. After leaving the stems out in the sun to dry, and soaking them in water you get a very soft wool-like substance.
I saw this done at a festival in Scotland. The cordage did not sting. Find out how to make string from stinging nettles without getting stung! Nettle cordage can be used for lots of things, such as fishing line and shelter building.