Interesting all the things I don’t know.I’ve been tying them for about 17 yrs. I have many thousands of flies laying around. Most are tied with feathers, fur and synthetics. Most of those bigger flies are for saltwater. The synthetics don’t absorb water so you can cast them easily without being heavy. I tie flies for some people here and there and donate some to worthy causes.
Yes some dry flies are made solely from feathers and thread. Most still have some fur too though.