Glassine is a very thin, smooth, water and air resistant paper. Glassine is grease resistant and used for envelopes, bookbinding, and packaging. Glassine envelopes are also used to carry pharmaceutical as well as coaine and heroin. glassine bags wre once used to package potato chips in the 20th century.
To make glassine, paper pulp is beaten to break down fibers. The pulp is pressed into molds and dried into sheets. The sheets are pressed through hot rollers, also known as calendering, and this makes the fibers lie flat and in the same direction. This process is repeated numerous times.
The basic color of glassine is almost transparent. The color can be changed with dyes or made opaque.