Having practically the same chemical composition as wool, it is made by mixing acid with skim milk. This extracts the casein, which looks like pot cheese. Evaporated to crystals, it is pulverized and dissolved into a molasses consistency, then forced through spinnerets like macaroni, passed through a hardening chemical bath, cut into fibres of any desired length. From 100 pounds of skim milk come 3.7 pounds of casein which converts to the same weight of lanital.* Readily dyed, it can be distinguished from wool only by experts, is mothproof.Aralac was said to be soft and serviceable, but customers complained that garments made from milk fiber smelled like sour milk when wet! Apparently, as the above image suggests, sweaters made from aralac also had the unfortunate effect of making your boobs look droopy. After the war, aralac production ceased as wool and cotton shortages abated. This probably explains why both sweaters and pointy, cone-shaped bras came into fashion in the 1950s.
*Images are from "Fabrics of the Future" by Robert D. Potter, The Science News-letter, February 7, 1940.