Ultra GSP is the strongest thread on the planet. Boasting steel-like strength for it's weight, this thread really lets you put the pressure on! Gel Spun Polyethylene is supple, ties flat and is available in three sizes. Choose 50 denier GSP for tying small trout flies with a minimum of bulk. GSP 100 has all around versatility for fresh and saltwater flies and GSP 200 is the size to choose for big deer hair work or when you really need to crank down! Sold here in white- if you need a colored thread for a head- use another thread to finish over top!