Mylar, also known as BoPET (Biaxially-oriented polyethylene terephthalate) is a polyester film made from stretched polyethylene terephthalate (PET) and is used for its high tensile strength, chemical and dimensional stability, transparency, reflectivity, gas and aroma barrier properties, and electrical insulation.
BoPET film was developed in the mid-1950s, originally by DuPont, Imperial Chemical Industries (ICI) and Hoechst. The term, ‘Mylar’, is presently a registered trademark of the DuPont - Teijin Corporation.
Because polyester film is less permeable to gasses than other plastics, it is often favored in the food packaging industry. When used as a laminate, e.g., aluminum foil / polyester / LLDPE, it provides increased shelf life and freshness, as well as an excellent barrier against moisture and gas, notably oxygen.
Vacuum metallization, also known as thermal evaporation, is the most common PVD (Physical Vapor Deposition) process used to apply metal alloys under vacuum. Where polyester film is concerned, aluminum is vaporized inside a vacuum chamber, and then bonded to a polyester sheet to achieve a uniform metalized layer. This process produces the silver-colored material often incorrectly referred to as "myar" by consumers, while the appropriate term is "metallized polyester".