I only use ruberized cork as a butt piece on spinning rods. When I build fly rods I usually use a mix of cork and burl, placing the harder burl rings where the most wear occurs (where the thumb and forefinger fall on the grip). I use either light mixed burl or natural burl. The natural burl is the natural color in the burls that most suppliers have in 5 different colors, blue, green, red, brown and natural. The natural is the lightest. I don't like solid burl grips because they are too heavy and too hard.