Properties of Mylar

By Catalina Bixler
Mylar, a polymer film, magnetic audio recording
cd-rom image by Nokomis from

A particularly strong industrial polyester film developed in the 1950s, Mylar or polyethylene terephthalate, quickly replaced cellophane during the 1960s. By the 1970s, the handling qualities of Mylar opened new consumer markets including photography, magnetic audio and video tape, electrical components, and medicine. Mylar allows for different applications such as coatings for solar reflective screens on its microscopically textured side (the other side is smooth). The properties of Mylar explain the useful diversity of this 21st century product.

Service Life

Known for its durability and strength, the service life of Mylar (American product name) depends on how much severe stretching and bending it experiences. Severe flexing is the time required to reach 10 percent elongation under different humidity and working temperature resulting in decreased service life. Typically, compromising the dimensional stability with too much strain, too much heat, or leaving Mylar in water too long also decreases the service life. Coating or enclosing Mylar prolongs its beneficial uses.

Heat Aging

Recommended temperature for Mylar is 302 degrees Fahrenheit for maximum service while retaining all properties. Severe or extensive heat exposure may require reducing service temperatures to Mylar. Heating Mylar 428 degrees Fahrenheit for 30 minutes costs nearly 10 percent of its tensile (bend and stretch) strength. Heated for less than a minute at 455 degrees Fahrenheit makes Mylar turn brittle and shatter. Special coatings to the film increases Mylar's resistance to heat.

Hydrolytic Stability

Over exposure to humidity under high temperatures causes decomposition of Mylar reacting to water (hydrolytic stability). Heating Mylar at 320 degrees Fahrenheit for four hours removes any damaging moisture absorbed by the film. Enclosing Mylar in an airtight container ideally frees the plastic film from of any over exposure to unwanted moisture.

Tensile Properties

Mylar's ability to stretch and return to its normal state (tensile strength) makes it a diverse product. Various temperatures affect the typical 38 hundreds ratio before yield and 58 hundreds after yield properties of Mylar. Using manufacturing guides included with the product allows for necessary adjustments and precautions when using Mylar under higher temperatures.


The scale of the load, the time applied, and temperature determines the "creep" or deformation of Mylar film. Under testing, Mylar shows no large levels of creep. In a 212 degree Fahrenheit oven after 4,000 hours, 35 hundred millimeter gauge and 50 100,000 lbs. per square inch Mylar experiences an insignificant creep of 9/10 percent.

Compressive Properties

Packaged in 1 inch by 1 inch cylindrical tubing, stacking or compressing reveals Mylar recording tape does not buckle, shatter, or fracture when tested under this standard warehousing and shipping application.

About the Author

Catalina Bixler's journalism career began in 1970. After five years as a publishing teacher, Bixler then published/edited NATO's U.S. 5th Army and 17th AF "Wiesbaden Post" newspaper. She holds a Bachelor of Arts in bilingual-journalism/community development from Redlands University, and a Master of Arts in adult education/training from the University of Phoenix.