Castelli nanoflex kneewarmercastellis nanoflex kneewarmers have an insert on the back in nano light fabric to help them bend around your knee better while keeping all the water protection intact these knee warmers are more comfortable due to more flexibility and in a slightly more compact package featureswater resistant thermal and breathable nano flex fabric nano light insert on back for extra stretch bringing better fit and comfort weight 102g pairtechnologiesnano flex exclusively