1. Gorilla Glass,durable and Scratch-resistant. 2. Multi-layer coating 3. Aluminum alloy frame, corrosion resistance. 4. 9H hardness,scratch without leaving a mark. Polarizing (CPL) Filter: 1. Polarizing filter eliminates reflections from non-metallic surfaces, and increases contrast and color saturation. 2. Removes unwanted reflections from surfaces such as water and glass. ND Filter: 1. Reduce an amount of visible light that enters the lens, allowing the user to utilize wider apertures or slower shutter speeds, particularly in bright conditions. 2. Work especially well for portraits by allowing the photographer to reduce the depth of field, producing pleasant background blur while keeping the subject in sharp focus. 3. Emphasize movement by permitting slow shutter speeds in bright light, giving life to photos that would otherwise look freeze in time. 4. This particular filter is multi-coated to minimize reflection on the filter surface, which reduces flare and ghosting, and produces sharp contrast and