Question: What Is Mylar?
You may be familiar with Mylar in shiny helium-filled balloons, solar filters, space blankets, protective plastic coatings or insulators. Here's a look at what Mylar is made of and how Mylar is made.
Mylar is the brand name for a special type of stretched polyester film. Melinex and Hostaphan are two other well known trade names for this plastic, which is more generally known as BoPET or biaxially-oriented polyethylene terephthalate.
Several properties of BoPET, including Mylar, make it desirable for commercial applications:
- electric insulator
- high tensile strength
- chemical stability
- gas barrier
- odor barrier
How Mylar Is Made
- Molten polyethylene terephthalate (PET) is extruded as a thin film onto a chilled surface, such as a roller.
- The film is drawn biaxially. Special machinery may be used to draw the film in both directions at once. More commonly, the film is drawn first in one direction and then in the transverse (orthogonal) direction. Heated rollers are effective for achieving this.
- Finally, the film is heat set by holding it under tension above 200 °C (392 °F).
- A pure film is so smooth it sticks to itself when rolled, so inorganic particles may be embedded in the surface. Vapor deposition may be used to evaporate gold, aluminum or another metal onto the plastic.