BCY Powergrip Bow String Center Serving is a blend of braided spectra and nylon. It is resin coated and grips extremely well. 60X Custom Strings has found powergrip to be very tough and super durable. For this reason this is our center serving material of choice. It has also proven to hold up very well on pesky cams that have a history of causing separation. It is available in 8 colors in .009, .014 or .018 diameters. If using for a center serving we would advise to go one size smaller then normal. This serving doesn't compress like others thus holding it's diameter.