Mylar is a trade name of DuPont Teijin Films of Hopewell, VA for biaxially-oriented polyethylene terephthalate (BOPET) polyester film used for its high tensile strength, chemical and dimensional stability, transparency, and electrical insulation. A variety of companies manufacture BOPET and other polyester films under different trade names, but Mylar is often employed as a generic designation for these, as in "Mylar capacitor" or "Mylar balloon."

History and manufacture

Mylar was developed by DuPont in the mid-1950s. In 1960, NASA launched the Echo satellite, a 100 foot (30.48 m) diameter balloon of metallized 0.005 inch (0.127 mm) thick Mylar film.

In manufacture, a film of molten PET is cast on a roll and subsequently stretched in and orthogonal to the direction of travel. One of its sides is microscopically smooth, while the other side contains microscopic asperities which promote adhesion of coatings and printing media.

Mylar can be aluminized , allowing reflection of up to 99% of light and heat. Like aluminium foil, aluminized Mylar has a shiny reflective side and a dull side. Mylar does not tear easily, like tin foil and aluminum foil. Its reflective properties enable it to be used as a solar viewer - commonly used for viewing events such as solar eclipses, although care must be taken because invisible fissures can form in aluminised mylar, reducing its effectiveness in this application.

Uses for Mylar

Common uses for BOPET films include:

• An overlay over a map, on which additional data, or copied data, can be drawn without damaging the map
• Performance sails for sailboats
• An electrical insulating material
• As base material for magnetic tapes (audio/video tape etc.)
• Insulation for houses and tents in a cold environment. A sheet of mylar covers the inner wall of the house or tent, with the shiny surface facing inward. This reflects body heat back into the house or tent, warming the interior more efficiently.
• Insulation for houses and tents in a hot environment. A sheet of mylar covers the outside wall of the house or tent, with the shiny surface facing outward. This reflects the sun's heat away from the house or tent, cooling the interior more efficiently.
• Mylar emergency blankets are used to reflect a shock victim's body heat back to the patient.
• Mylar solar curtains reflect sunlight and heat away from windows.
• NASA uses five layers of mylar in spacesuits to keep astronauts warm and radiation resistant.
• Mylar balloons are used for floral arrangements and parties.
• Mylar foil is used as a mirror-like decorative surface on some book covers, T-shirts, and other flexible cloths.
• Mylar foil is, along with other plastic films, used as a dielectric in foil capacitors.
• Very thin Mylar is often used as the diaphragm material in electrostatic loudspeakers.
• Mylar has been used in the production of drumheads since 1958 due to its durability and acoustical properties when stretched over the bearing edge of the drum. They are made in single- and double-ply versions, with each ply being between 2mil and 10mil (1 mil=0.0254 millimeter) in thickness, with a clear or opaque surface.