Most circular filters are made of a brass/aluminum frame, but these kind of materials are heavy and not ideal under cold weather conditions. Because of that, NiSi created a Titanium Alloy Frame Pro Nano UV Cut -395. It's made of Titanium Alloy Frame with Nano coated optical glass. They feature a lightweight and durable design.Titanium Alloy Frame is light, hard, anti-corrosive, heat-resisting and with good performance under very low temperature. The density of Titanium is 4.54g/cm, it's almost half of the volume of the same weight steel, and the hardness is twice of aluminum. Its anti-corrosion ability makes it able to endure strong acid and base. Its melting point is 1942K, about 1000k higher than gold and 500k higher than steel.Lens Standard Optical Glass Lens standard optical glass H-K9L is high homogeneous with super low impurity and has good physical and chemical performance. It is usually processed to a high precision optical element such as a lens, prism, plane mirror, etc.UV Cut Nano Coating Nano coating cut the UV light below 395nm, and effectively avoid a soft image. It makes sure high transmittance and ultra-low refiection on the glass surface. It enables the visible light to come through evenly and control the color balance. Also, there's a super strong waterproof coating with anti-scratch ability. It's easier to remove the dust, fingerprint, water stains, and keep the filters clean.Matte Black inside the frame using electroplating