Denier is defined as the mass in grams per 9,000 meters
70 Denier = 70 grams per 9000 meters yarn.
UTC Ultra Thread 70 Denier
This is a great size for tying the smallest of flies and for tying with low bulk on larger flies. It is the ideal choice for dry flies, nymphs, and midges size 14 or smaller.
100 yds. spool.