Winston Cork
Not to disagree with other postings, but rather to relate my own experience with Winston: I own 11 of their rods; 2 B2X speys, 3 GVX specials (the sweetest dry fly rod I have cast), and 6 B2X's single handers. The cork has held up well after in some cases many years of abuse. While I am not an expert on cork, Winston's is the equal to the cork on a high end custom J D Wagner bamboo rod, and a whale of a lot better than the cork on even some of my more expensive "name brand" imported rods.
HTH
Jim