Dubbing wax is a must-have for any fly tyer.
Working with fine dubbings or other slippy materials (flash etc.) is just so much easier, when adding a bit of wax to your tying thread.
Whether you're dubbing on the thread directly, with the split-thread-technique or in the loop.
Veniard's Prepared Fly Tyers Wax is a true classic and its recipe hasn't changed at all over the years.
This is why it's so popular amongst famous fly tyers like Davie McPhail and many others.