Seals fur
The best material for many flies: lake hoppers imitating emerging/adult chironomids, sedge hogs imitating caddis/sedge flies, wooly buggers, shrimp patterns.
It is translucent and acts like a fiber optic giving a glow to the fly.
For dry flies seals fur keeps the fly floating for a longer period of time, cast after cast.
Due to the availability limitations, the natural undyed seals fur may be a good option and then dying to your desired color. We also sell Veniard dyes which are the best for getting all the colors needed for the most popular flies.