Buy a little bottle of silicone water-proofer made for shoes.
Cavalier' is one brand name, available at Walmart. When you finish
tying a batch of dry flies, dip them in it, or paint them with it
using a small brush, and let them dry overnight.

You don't have to mess around with "greasy kid stuff" while on the
stream.

Alternative: Buy a can of Thompson Water seal. Do the above.

vince