Loon also makes something called Hard Head which I've been using for a couple of weeks now. Personally, I think I would open a window instead of skipping the use of flexament or another traditional because while I know that they will soak into a thread head, I don't quite know that the same can be expected of something like Hard Head although I suspect it would work about as well. Hard Head comes in several colors as well as a clear formula. The stuff works well, builds up a crystal clear head, and winds up plenty hard. The only drawback to it is that its rather expensive, the cost being over $6 for what I believe is a 1oz bottle. It gives off no vapors that I've noticed, and Loon seems to be very good about putting out products which are environmentally friendly.
Devcon 5 minute epoxy can pull off the same sort of trick. If I'm only coating one head, I'll normally go with the Hard Head, but if I'm working in bulk, the Epoxy wins out simply because of the fact that its so much cheaper and it works just as well. There are a couple of tricks that make working with Epoxy a bit less frustrating and will cause the heads of your flies to yellow less. First off, only mix epoxy on white paper. Any coloration in the surface you're mixing on can cause color to be absorbed into the mixture. Secondly, don't use a toothpick to do the mixing. I always use an unfolded paper clip to mix with. Again, the reason for this is that the wood toothpick will discolor the Epoxy a bit as well. The bottom line with Epoxy is that its going to yellow over time regardless of what you do with it. In my case, I go through enough flies that this is not a concern - I've lost them before having a chance to see them go yellow. If you plan on making flies you'll be holding on to for a loooooong time like for display purposes, go with Hard Head. If you're just making flies to fish with, I'd say open a window and break out the Epoxy. Hope this helped! John Roth
