DT double tapered fly line

It is tapered evenly at both ends, as opposed to the weight forward line. Double tapered lines are the heaviest along their entire length but will still fall within the AFTMA specifications for the first 30 feet of the line. Notice that this line has no proper "front end" to it.Double tapered lines are often a beginner's first line. They are better for mending than a line with a shorter head and they can be turned around on the reel if needed. They can also make longer roll casts than the weight forward lines 

Double Taper Fly Line Structure Specification