In the early 1940s, vinyl plastic emerged as a highly versatile material for a wide range of applications, from shower curtains to cable insulation. Making it work for tape, however, was a different story. A major ingredient in vinyl film was tricresyl phosphate (TCP), which was used as a plasticizer. Unfortunately, TCP tended to migrate, giving the surface of the vinyl film an oily quality and degrading every tape adhesive known. Research chemists and engineers at 3M™ set out to create a dependable, pressure-sensitive tape made of vinyl film that would have the required electrical, physical and chemical properties. Experiments were conducted combining new plasticizers with the white, flour-like vinyl resin. Finally, in January 1946, inventors Snell, Oace, and Eastwood of 3M™ applied for a patent for a vinyl electrical tape with a plasticizer system and non-sulfur-based rubber adhesive that were compatible. The first commercially available version of the tape was sold for use as a wire-harness wrapping. Interestingly, this original black tape wasn't black at all. Tapes formulated for high-temperature were yellow, and later versions were white. White tape, because of its instability in ultraviolet light, was eventually replaced with black tape, although colored vinyl tapes are still used as identification and marking tapes. Black became the standard industry color for vinyl standard tape, primarily because of its ultraviolet resistance. Thicknesses originally were 4-mil, 8-mil and 12-mil caliper. These were standardized to 7-mil and 10-mil in 1948.
