Gyroll inserts are 2mm fin socks with a fin heel pad in one! The sock is attached to the fin by a Velcro pad that wraps around the heel of your fin to give your feet comfort and protection. Viper/Gyroll inserts are completely removable /changeable, with sizes to fit a wide variety of open heel fins. They are vented to drain sand and also work with the Gyroll connector fin savers.