The highly protective Sigma WR Ceramic Protector filter is constructed from Clear Glass Ceramic, an extremely tough crystallized glass, and therefore delivers outstanding strength. It features the high transmittance required of optical devices whilst combining greater hardness than chemically strengthened glass and greater flexibility than sapphire crystal glass. Its outstanding protective capability is leading to high reliability. By combining much greater hardness than chemically strengthened glass and greater flexibility than sapphire crystal glass. Clear glass ceramic is the ideal material for protective filters that achieve over 10 times the strength of a conventional protective filter. Works first Clear Glass Ceramic Protective lens filter. High transmission optical glass, Extremely tough construction with chemically strengthened glass, Highly shock resistant, Scratch resistant, Thinner and lighter design, Water repellent coating, Minimises flare and ghosting.