Demon Eiger photochromic lenses 2 to 4 are sunglasses suitable for all outdoor activities, from glacier to hiking. Photochromic lenses 2-4 are outstanding lenses with a light grey base tone that can reach class 4 at times of increased activity. The light initial grey allows you to see correctly in shaded and low light areas, and with the best lighting conditions and UV exposure can reach class 4, typically used in mountaineering.Photochromic lenses 2-4 subjected to UV radiation and general sunlight initiate a reversible chemical reaction that blackens the lens surface until it reaches class 4 (if necessary). When exposure to light and UV ceases, the lens gradually returns to its original state of colour.This special photochromic lens was designed with the aim of creating a variable lens for Hikers and Mountaineers, which would adapt to every light variation on their route. Whether in a wooded area, or on a slope in semi-darkness, the lens is designed to lighten and darken quickly, allowing the athlete constant and perfect vision.The initial tint of the lens is a subtle shade of smoke that does not force the athlete to remove the glasses in places with low light. Likewise, class 2 prevents glare when coming out of shaded areas. The attainment of class 4 at the time of maximum effort is influenced by the intensity of UV and light.It is important to understand that this particular lens is designed to reach class 4 only when necessary, thus avoiding too dark a view of the path.The frame is made of TR90, TR90 is a special composition of Nylon and carbon fibre used by DEMON for the creation of all its Mountain, Trekking and Mountaineering goggles. It is an allergen-free composition and can be used in extreme conditions even over long periods without causing irritation to the skin.The uniqueness of TR90 is its extraordinary flexibility and hardness against unintentional impacts and mechanical dragging, and it is also 20 per cent lighter than frames made of classic materials. Normally, a frame made of this particular composition weighs between 20 and 45 grams, depending on the thickness of the frame.The non-slip Megol portions are made of soft, ultra-light and hypoallergenic material that makes weight the main feature. These parts are designed to increase the comfort of the glasses and prevent any uncomfortable downward movement of the nose, especially at times when maximum stability of the glasses to the face is required.The sweat sponge for the mountain goggles is made of high-density hypoallergenic material. A must for mountaineers, it performs several functions. Protection from perspiration: prevents drops of perspiration from coming into contact with the eyes during heavy exertion. Protection from air and projections: Prevents air or any projections (e.g. dust) from coming into contact with the eyes. Protection from light: Prevents lateral light rays from coming into contact with the eyes, preventing proper vision. The sweat sponge is removable at will and is used by the mountaineer or hiker as required.Elastic strap: for the Eiger model, included is a removable elastic strap. It is made of flexible material to provide greater comfort and safety, even in extreme conditions and over rough terrain. In addition, it ensures a firmer and tighter grip on the head, in order to protect the eyes from: air, cold, dust and various debris that the athlete may encounter on his way.The mountain goggles with photochromic lenses for Mountaineering and Hiking guarantee maximum performance without any sacrifice.The measurements of the Eiger goggle are:Width - 140mm;Height - 50mm;Rod Length - 125mm;Lens Base - 8. Demon Eiger mountaineering sunglasses