Discraft says this about the Zone (Soft): Discraft Stability Rating: X-Line 2.0
The Zone (Soft) is an overstable low profile, small diameter putt and approach disc. For players who like an overstable putter for hyzer arch putts and short drives. Very predictable as an approach disc as well. The X-Line plastic mutes skip and softens impact.
About X-Line Plastic
High durability, excellent grip, even when wet, more consistent flights.