UNI-Cord (8/0 and 12/0) is an extremely strong ( for the same diameter it is twice as strong as Kevlar) fly-tying thread manufactured of continuous fibers of gel-spun polyethylene (GSP). It is considerably more expensive than other threads and so is reserved for unusual situations where a fine but very strong thread is required.
8/0 has strength of 85 denier, and 12/0 strength is 50 denier.
UNI-Cord comes on 50-yard (ca. 45 metres) spools. Unwaxed.