Castelli thermoflex knee warmercastelli concentrate on getting everything almost perfect when it comes to warmers and with these thermoflex knee warmers they may have just cracked the magic formula warm and flexiblethe fabric is extra warm and flexible while the fit eliminates any extra fabric the silicone gripper at the top of the knee warmers prevent them from slipping down your leg and the cross wrap cuffs at the bottom provide you with extra snugness featuresthermoflex soft fleece fabricc