The milk protein casein was made into fibers on an industrial scale as early as the 1950s and was available in the commercial names such as Lanita produced from Snia and Fibrolane produced from Courtalds [07Hea]. Trade names of casein fibers also varied by the country where the fibers were produced. For example, casein fibers were marketed as Aralac and Caslen (USA), Lactofil (Holland), Cargan (Belgium), Tiolan (Germany), Silkool (Japan), and Fibrolane (England) [51Tra]. Traditionally, casein fibers were produced by dissolving casein in alkaline solutions, extruding and coagulating using sulfuric acid and sodium sulfate and later cross-linked with aluminum sulfate and formaldehyde, and finally treated with metal salts such as zinc [69Sal]. Although most reports do not provide the properties of the fibers, it has been suggested that casein fibers had dry tenacity of 0.8–1.0 g/den, wet tenacity of 0.4–0.5 g/den, and elongation of 30–50 % [69Sal]. However, the fibers were soluble to weak alkali and to enzymes and therefore not practically useable. In addition, yellowing of the fibers was observed when fibers were treated with alkali at 70 °C for 40 min, but the fibers were stable under acidic conditions. Casein fibers were reported to have good uniformity, less impurity, and superior spinnability, but the fibers had poor cohesion and frictional resistance necessitating a pretreatment before the fibers could be made into yarns of 136 tex. The protein fibers were dyed with reactive dyes and found to have uniform dyeability.