The Lee Warming Filter Set consists of 4 polyester 4x4" warming filters; 81, 81B, 81D and 85C. The Gel Snapis Lee's easy and affordable filter holder. Simply insert your 4 x 4" filter, snap it shut, and "snap" it on to any lens 82mm or smaller using the included "Elastomeric Tension Device", also known as an "E.T.D.", i.e, rubber band.