From the Manufacturer...
The JK (Juliana Korver) Aviar is made from the driver mold in a special blend of durable Pro-line Plastic that is more flexible and grippier than the other Aviar models. It has the same flight characteristics as the KC Aviar. Its softer plastic is better in colder climates and for those who have dry hands and require a tackier grip.
Weight Range: Pro: 160-175g
Best Choice for: Inside putter, Accuracy approaches, Beginners
Available Plastics: Pro