What is that red plastic-like covering that some early tennis balls were encased in?

An early attempt to lengthen the life of tennis balls after leaving the factory, was to contain them in a viscose wrapping. Viscose is a viscous organic liquid used to make rayon and cellophane. Two half covers of this material are fitted around a ball, overlapping in the center. The wet solution fits loosely around the ball. In drying out, viscose contracts and compresses the ball, relieving it from the strain of the inflation pressure. When the cover is removed, the ball resumes its normal size and liveliness.