I was given a pattern book back in 1986 titled 50 Favorite Dry Flies by Donald Overfeld. That was when I first learned of the actual TUPS dubbing. Years later some guys were discussing this dubbing on another site and one guy in particular went to the extreme of researching and duplicating the dubbing based on the original formula. I was fortunate that he sent me a ziplock bag of that stuff and provided the formula. I still have that batch and I use it as a basis when making more.
Anyway, what I found was that it makes an excellent March Brown(eastern) emerger, dun, and wet fly. I am pretty sure that the transluscent blend is what makes the dubbing so effective. So I took the blend and made it about 2 or 3 shades lighter that yielded dubbing for a light Hendrickson and similarly colored flies. Still another 2 shades lighter and a light Cahill. Going the other way into the 'browns' or 'olives' worked too. The only thing was, any fly smaller then size 16 was tough to dub.
Here's a link with information about the dubbing. Not sure about the 'unborn seal' though!
What do you guys think?