This moldable tungsten putty is a great way to get your flies down fast.
Add it to the head of your fly to turn a standard nymph or streamer into a weighted fly much like a beadhead.
Use it in place of split-shot, but, unlike spit-shot, it can be molded into thin tapered cigar shape that minimizes hang-ups. The streamlined shape also cuts through the water easier giving a faster sink rate and less drag.
To apply, warm a small bit of putty between your fingers to soften it. Apply as desired, and dunk into the water to cool and harden the putty. To remove, simply warm between your fingers again. It will once again become soft and pliable.
To create the tapered cigar mentioned above, flatten into a disk, fold the disk over the leader and then roll between your fingers to create a the taper. Apply the putty over the knot between your leader and tippet to prevent it from slipping down the line.