The Properties of Cellophane

French chemist J.E. Brandenberger developed cellophane from plant cellulose in 1908 while researching ways to make fabrics repel dirt. The transparent wrapping material is chemically identical to rayon, but is formed into a thin film by forcing it through a narrow slit into a bath of sulphuric acid before further processing to make it flexible and moisture-resistant.

In an era before plastic film, there was heavy demand for an inexpensive, transparent packaging material. Cellophane is transparent to the visible spectrum of light, and also allows approximately 70 per cent of ultraviolet rays between the wavelength of 2900 and 3100 angstroms to pass through. It loses only a small amount of its transparency after continuous exposure to ultraviolet light over a long period, making it useful for long-term storage of packaged items.

Untreated cellophane is semi-permeable, and is used in several scientific procedures to filter and separate compounds in solution. Moisture-proof cellophane, treated with a coating of water-resistant lacquer, has a very low diffusion rate, allowing only 270 mg of water vapour per square meter per hour to pass through at temperatures of 37.8 degrees Celsius. The material first gained popularity as a wrapping to moisture-proof cigarettes and cigars. It is also an effective barrier against microorganisms.

Cellophane was introduced in the early 20th century as an alternative to paper wrapping material. It was considered to be superior both for its transparency and its strength -- cellophane has higher tensile strength than the all-rag bond paper used at the time, and bursting strength comparable to the best-quality paper available. It is available in thicknesses ranging from 9/10,000 inch to 7/1,000 inch.

Cellophane has an interesting optical property called birefringence. When placed between two sheets of polarising material, cellophane molecules act as tiny prisms, emitting coloured light when white light passes through them. This characteristic, more common in crystalline structures like quartz, has led some artists to use it in interactive artwork, since changing the angle and orientation of the polarising material and the cellophane changes the appearance of the resulting light.