I'm no rod building expert but I know what I like to cast, and cork is hard to beat. First off there is a certain warmth and slight compression in the hand with good cork that is missing in a denser material like wood, and on cold or wet days or when gloves are called for it might be a factor.
Another thing to think about is flex, I can feel the blank flexing under the cork when I drive a Spey cast for distance.
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