What are mylars used for?

I’ll never forget the first time I saw a picture of the Apollo Lunar Module. As a kid obsessed with rockets and engineering, it wasn’t the strange, spider-like legs or the tiny windows that fascinated me. It was the skin. It was wrapped, almost messily, in what looked like gold and silver foil. It seemed so fragile, like something you’d use for a school project, not a machine designed to fly through the vacuum of space.

“What is that stuff, Dad?” I asked.

He was a mechanical engineer and thought for a moment. “They call it a space blanket, but it’s a special kind of plastic film. I think it’s called Mylar. It’s tougher than it looks. A lot tougher.”

That word—Mylar—stuck with me. Years later, working in product design and manufacturing, I would come to understand the profound truth in his words. That flimsy-looking “foil” is one of the most versatile and high-performance polymer films ever created. It is the secret skin inside our motors, the protective barrier for our food, and the reflective shield that can keep us from freezing to death. But it isn’t foil at all. It’s a precisely engineered plastic, and understanding its true nature is the key to unlocking its incredible potential.

Answer-First Summary: What Are the Primary Uses of Mylar?

Mylar® is the brand name for a specific type of polyester film called Biaxially-oriented polyethylene terephthalate (BoPET). Its unique combination of properties makes it indispensable across numerous industries. Here’s a quick overview of its main properties and the applications they enable:

What Exactly Is Mylar Plastic?

Before we can understand what Mylar is used for, we have to understand what it is. Most people interact with it in its metallized form—the shiny silver of a birthday balloon or the inside of a chip bag—and assume it’s a type of aluminum foil. This is the most common misconception.

Mylar is 100% plastic. Specifically, it’s a polyester film made from polyethylene terephthalate (PET), the same polymer family as soda bottles. The magic, however, isn’t in the raw material but in the manufacturing process. The film is created through a process called biaxial orientation.

Imagine you have a warm, thick sheet of plastic dough.

1. First, it’s stretched in one direction (the machine direction). This pulls the long-chain polymer molecules into partial alignment, like combing tangled threads.
2. Then, while being held taut, it’s stretched in the perpendicular direction (the transverse direction).

This second stretch forces the polymer chains into a tightly interlocked, crystalline structure. This molecular alignment is what transforms a standard, flimsy piece of PET plastic into the incredibly strong, stable, and clear film we know as Mylar. The metal shine that we see on balloons or space blankets is an afterthought—an ultra-thin layer of vaporized aluminum deposited onto the surface of the clear Mylar film in a vacuum chamber. This metallization gives it its reflective properties, but the strength, toughness, and stability all come from the underlying plastic film.

Why Is Mylar Such a Good Electrical Insulator?

One of Mylar’s first and most critical industrial applications was in the world of electronics and electricity. All plastics are insulators to some degree, but Mylar’s properties make it exceptional. Its high dielectric strength means it can withstand a very high voltage before it breaks down and allows electricity to pass through.

I spent a summer working for a company that rewound large industrial electric motors. The heart of the job was painstakingly inserting new copper windings into the laminated steel core, called the stator. My mentor, a grizzled old technician named Frank, handed me a roll of translucent, milky-white tape. “This is the most important part of the whole job,” he said. “It’s Mylar. Don’t tear it.”

My job was to cut precise liners from the Mylar sheet and use them to line the slots in the stator before the copper wire was inserted. The Mylar liner created an impenetrable electrical barrier between the copper windings and the steel frame of the motor. It prevented catastrophic short circuits that would instantly destroy the motor. Its toughness meant we could pack the copper wires in tightly without fear of puncturing the liner, and its thinness allowed for a maximum amount of copper to be used, making the motor more powerful. This application—known as “slot insulation”—is a perfect example of Mylar’s role as an unsung hero in the electrical world.

What Gives Mylar Its Incredible Strength and Stability?

When an architect or engineer in the pre-CAD era drew a blueprint, they needed a medium that wouldn’t change. A paper drawing would shrink, stretch, and warp with the slightest change in humidity, throwing critical dimensions off. The solution was drafting film made from Mylar.

Because of the biaxially-oriented molecular structure, Mylar is dimensionally stable. It doesn’t absorb moisture from the air, and its coefficient of thermal expansion is low. A line drawn to be exactly 12.000 inches long would remain 12.000 inches long, whether it was a dry winter day or a humid summer afternoon.

This same combination of strength and stability makes it the undisputed king of flexible packaging. A bag of potato chips needs to be strong enough to not puncture easily, stiff enough to hold its shape, and stable enough to provide a perfect surface for high-quality printing. The shiny layer inside is often metallized Mylar laminated to other plastics, providing a combination of strength, barrier properties, and visual appeal. The next time you struggle to tear open a bag of snacks, you are fighting against the incredible tensile strength imparted by that biaxial orientation process.

This incredible combination of electrical, mechanical, and chemical properties makes Mylar a foundational material in modern engineering. But what happens when you coat it with a mirror-finish layer of metal? It takes on an entirely new identity, one that can shield us from the cold of space or the heat of the sun.

That flimsy-looking emergency “space blanket” in a first-aid kit works on the exact same principle as the multi-million-dollar shielding on a satellite. It’s not about keeping the cold out; it’s about keeping your heat in. Understanding how it accomplishes this is to understand a fundamental secret of the cosmos.

How Does Metallized Mylar Control Heat?

To grasp Mylar’s thermal magic, we need a quick physics lesson. Heat moves in three ways:

1. Conduction: Direct transfer through touch. A hot pan handle heats your hand through conduction. Metals are good conductors; a foam coffee cup is a poor conductor (an insulator).
2. Convection: Transfer through the movement of fluids (like air or water). A cold wind chills you because moving air carries heat away from your body. A double-pane window works by trapping a layer of air, stopping convection.
3. Radiation: Transfer through electromagnetic waves. This is how the sun heats the Earth across the vacuum of space. You can feel the radiant heat from a campfire even from several feet away.

Traditional insulation, like the pink fiberglass in your attic or the foam walls of a cooler, is designed primarily to stop conduction and convection. It’s bulky and filled with tiny air pockets. The material itself is a poor conductor, and the trapped air prevents convection currents from forming. It works very well, but it’s completely useless against the primary heat source in the solar system: radiation.

This is where metallized Mylar shines, literally. Every object with a temperature above absolute zero is constantly emitting thermal radiation. Dark, matte surfaces are very good at this; they have high emissivity. A black cast-iron radiator is designed to be an efficient emitter of heat. Shiny, mirror-like surfaces are the opposite; they have very low emissivity.

A sheet of metallized Mylar has an emissivity of around 0.03, meaning it radiates only 3% of the heat that a perfect black object would at the same temperature. Furthermore, it has a reflectivity of about 97%. When you wrap yourself in a Mylar space blanket, two things happen simultaneously:

• Your body heat, which is trying to escape as thermal radiation, hits the inside of the blanket and 97% of it is reflected right back to you.
• The outer surface of the blanket, being a poor emitter, is very slow to radiate whatever heat does make it through to the cold air around you.

It’s a two-pronged thermal attack. It is not an insulator in the traditional sense—you can feel the cold right through it if you press it against your skin (conduction). But as a barrier to radiant heat, it is nearly perfect.

Mylar vs. Traditional Insulation: Which Is Better?

This question is a bit of a trick, as they solve two different problems. A direct comparison, however, reveals their unique strengths and weaknesses and why they are often used together in high-performance systems.

The key takeaway is that Mylar isn’t a replacement for fiberglass; it’s a powerful supplement. In home construction, a radiant barrier installed in an attic with an air gap below it can reflect a huge portion of the sun’s radiant heat before it ever gets a chance to be absorbed by the fiberglass insulation below. They are a team.

What Is the James Webb Space Telescope Sunshield Made Of?

For the ultimate case study in Mylar’s power, we look to the most advanced telescope ever built: the James Webb Space Telescope (JWST). Its mission is to detect faint infrared light from the earliest stars and galaxies. To do this, its scientific instruments and mirrors must be kept cryogenically cold, at a temperature below -370°F (-223°C). The problem? The sun, Earth, and moon are constantly bathing it in thermal radiation.

The solution is a tennis court-sized, five-layer sunshield. Each layer is thinner than a human hair and made of a Mylar-like film called Kapton (chosen for its even better performance at extreme temperatures), which is then coated with aluminum and doped silicon.

Here’s how it works:

• The first layer, facing the sun, reflects the vast majority of the incoming solar radiation back into space.
• The small amount of heat that gets through is then radiated into the gap between layer one and layer two.
• The second layer, now much cooler, reflects most of that heat out into space from the sides.
• This process repeats for all five layers. Each successive layer is significantly cooler than the one before it.

The vacuum of space between each layer is the perfect “air gap,” preventing any heat transfer via conduction or convection. By the time the residual heat gets past the fifth layer, it’s so minuscule that the telescope’s instruments can easily maintain their frigid operating temperature. The entire, massive sunshield weighs only a few hundred pounds and provides an effective Sun Protection Factor (SPF) of over 1,000,000. It is the most perfect and critical application of radiant barrier technology ever conceived, and it relies entirely on the principles pioneered by that simple, shiny Mylar film.

Are There Different Types of Mylar Film?

Just as “steel” is a generic term for a huge family of alloys, “Mylar” is the starting point for a vast range of specialized films. The base BoPET film can be manufactured in various thicknesses, typically measured in mils (thousandths of an inch) or gauge.

• 100 gauge (1 mil): Common for balloons and light packaging.
• 48 gauge (0.5 mil): Often used in space blankets.
• 700 gauge (7 mil): A more rigid film used for stencils or electrical insulation.
• 1400 gauge (14 mil): A very thick, almost sheet-like material.

Beyond thickness, the film can be treated with different coatings to enhance specific properties. There is Mylar with print-receptive coatings for graphic overlays, anti-static coatings for protecting sensitive electronics, UV-blocking coatings for archival applications, and dozens of other variations. The specific grade is chosen to precisely match the demands of the application, whether it’s protecting a comic book or a billion-dollar space telescope.

We’ve seen Mylar’s incredible strength and its unparalleled ability to control heat. It seems like a super-material with no downsides. But that’s never the case in engineering. What are its weaknesses? How does it degrade over time, and what are the common mistakes people make when designing with or using this versatile film?

But no material is perfect. Every superhero has a kryptonite, and every engineering material has a set of weaknesses that you must understand and design around. Ignoring these limitations is the fastest way to turn a brilliant design into a catastrophic failure. I’ve seen projects fail because a Mylar component, specified for its strength, was placed in direct sunlight for a year. I’ve seen insulation systems that didn’t work because the installer didn’t understand the fundamental physics of a radiant barrier.

These failures all stem from a single root cause: a partial understanding of the material. To truly master Mylar, you need to know not only what it can do, but also what it cannot. These are the non-negotiable commandments of working with this remarkable film.

What Is Mylar’s Greatest Environmental Weakness?

Commandment #1: You Must Respect Ultraviolet (UV) Radiation.

This is the single most important limitation to understand for any long-term application. The very same sunlight that Mylar so effectively reflects contains high-energy ultraviolet radiation, and that radiation is a poison to the long polymer chains that give Mylar its strength.

The chemical name for Mylar is polyethylene terephthalate (PET). This consists of long, repeating chains of molecules, tangled together like a bowl of microscopic spaghetti. This entanglement is the source of its toughness. UV photons, however, are like tiny scissors. When they strike the polymer, they carry enough energy to break these chains. Initially, the effect is invisible. But over time, as more and more chains are broken, the material begins to lose its properties. It becomes brittle, loses its tensile strength, and will eventually yellow and crumble into dust.

A Mylar balloon left outside after a party provides a perfect, accelerated demonstration of this process. In a few days, the once-resilient film becomes so fragile that a slight breeze can cause it to shatter. This is why standard Mylar is a poor choice for applications like long-term greenhouse glazing or permanent outdoor banners.

To combat this, manufacturers produce UV-stabilized or UV-inhibited grades of Mylar. These films have special additives blended into the polymer that are designed to absorb UV radiation and dissipate it as low-level heat, protecting the polymer chains from damage. When you specify Mylar for any application with prolonged sun exposure, you must ensure you are using a UV-stabilized grade, or your project is doomed to a premature, brittle failure.

Is High Tensile Strength the Same as Toughness?

Commandment #2: You Must Differentiate Between Tensile Strength and Tear Resistance.

This is a subtle but critical distinction. We’ve celebrated Mylar’s incredible tensile strength—its ability to resist being pulled apart. A 1-inch wide strip of 7-mil Mylar can withstand hundreds of pounds of force. But its resistance to tearing is comparatively low.

Imagine trying to tear a phone book in half by pulling on the covers; that’s tensile strength, and it’s nearly impossible. Now, imagine starting a small tear in a single page and pulling; that’s tear propagation, and it’s effortless. Mylar behaves in much the same way. It is very difficult to initiate a tear in the middle of a sheet, but once a nick or puncture occurs at an edge, a tear can propagate across the entire sheet with very little force.

This is a critical consideration for applications like tarps, sails, or packaging. A sharp object creating a small puncture can compromise the integrity of the entire sheet. Designers account for this by reinforcing edges, using ripstop patterns (where a grid of stronger fibers is woven into the material to stop tears from propagating), or by laminating the Mylar to a tougher, more tear-resistant substrate like nylon fabric. Never assume that its high tensile strength makes it indestructible; its Achilles’ heel is a sharp point and a started tear.

How Can Mylar Insulation Make You Colder?

Commandment #3: You Must Provide an Air Gap for Radiant Barriers.

This is the most misunderstood principle of using metallized Mylar for insulation, and it’s a direct consequence of the laws of thermodynamics. As we discussed, a radiant barrier works by reflecting thermal radiation. For this to happen, there must be a space for that radiation to travel across.

If you take a Mylar emergency blanket and press it directly against your cold, wet skin, you will get colder, faster. Why? Because you have eliminated the air gap. Instead of reflecting your body’s radiant heat, the thin aluminum layer is now in direct physical contact with your skin, and it becomes a conductor. Since aluminum is an excellent conductor of heat, it will rapidly pull warmth from your body into the cold material, a process called conduction.

To work effectively, a radiant barrier must have an air gap of at least 3/4 of an inch (about 2 cm) between it and the next surface. In a building, this means leaving a space between the radiant barrier and the bulk insulation. In an emergency blanket, it means fluffing it up and creating a pocket of air between you and the blanket. Without that gap, your high-tech radiant barrier is nothing more than a useless, conductive sheet of foil.

Can You Clean Mylar With Anything?

Commandment #4: You Must Verify Chemical Compatibility.

While PET is a relatively non-reactive polymer, it is not invincible. It has excellent resistance to water, oils, and most acids, which is why it’s used extensively in food packaging. However, it can be attacked and damaged by strong alkalis (like sodium hydroxide), certain chlorinated solvents, and phenols.

For most consumer applications, this is rarely an issue. But in an industrial setting, it’s a critical design factor. If you are designing a Mylar graphic overlay for a control panel in a chemical plant, you must know what cleaning agents or accidental spills it might be exposed to. Using the wrong cleaner could cause the surface to haze, craze, or even dissolve. Always consult a chemical compatibility chart from the manufacturer if the Mylar will be used in an environment with anything more aggressive than soap and water.

Why is Mylar Dangerous Around Sensitive Electronics?

Commandment #5: You Must Control Static Discharge.

Mylar is an excellent electrical insulator. This is a benefit when it’s used to insulate motor windings or capacitors. But this same property means it is prone to building up a significant static electrical charge, a phenomenon known as the triboelectric effect. You’ve experienced this when a Mylar balloon sticks to your hair.

In most cases, this is a harmless annoyance. But in an environment with sensitive electronics or flammable vapors, it’s a massive hazard. A static discharge from a sheet of Mylar can easily be several thousand volts, more than enough to destroy a microchip or ignite a solvent-rich atmosphere.

This is why you will never see standard Mylar used to wrap a new hard drive or motherboard. For these applications, manufacturers produce specially treated anti-static or static-dissipative films. These films have a transparent, conductive coating (often an indium tin oxide layer) or are impregnated with conductive particles. This allows any static charge to safely bleed away to ground rather than building up to dangerous levels. If you are working with electronics, packaging powders, or operating in a flammable environment, using anti-static Mylar is not optional—it is a fundamental safety requirement.

Conclusion: Understanding the Complete Material

Mylar is not just a single product; it’s a platform. It’s a foundational material whose core properties of strength and stability can be augmented with coatings and treatments to create a thousand different solutions for a thousand different problems. It can be a simple, strong drawing film, or it can be a multi-layered, vacuum-deposited shield that protects our most advanced scientific instruments from the raw power of the sun.

But like any powerful tool, its effectiveness is defined by the user’s knowledge. By understanding not only its strengths but also its weaknesses—its vulnerability to UV light, its low tear resistance, its absolute need for an air gap, its chemical sensitivities, and its tendency to build static—you move from a casual user to a skilled practitioner. You learn to design with the material, not just specify it. And in doing so, you unlock the full potential of one of the most versatile and essential materials of the modern age.

Frequently Asked Questions (FAQs)

1. Is Mylar food-safe?
Yes, Mylar (BoPET) film is overwhelmingly considered food-safe by regulatory agencies like the FDA. It is chemically stable, non-toxic, and does not leach harmful chemicals into food. This is why it is one of the most common materials used in food packaging, especially for products that require a long shelf life, like coffee bags, chip bags, and military MREs (Meals Ready-to-Eat), where it acts as a superior barrier to oxygen and moisture.

2. Can you recycle Mylar?
Technically, Mylar is made from PET, which carries the #1 recycling symbol. However, in practice, most Mylar products are very difficult to recycle through standard municipal programs. This is because it’s often a very thin film that can jam sorting machinery, and it’s frequently laminated with other materials (like aluminum foil or other plastics), making separation impossible. While pure, thick PET film can be recycled, the vast majority of consumer Mylar products end up in landfills.

3. What is the difference between Mylar and Kapton?
Both are high-performance polymer films, but they serve different purposes. Mylar (PET) is known for its strength, stability, and low cost. Kapton (polyimide) is a specialty polymer that is prized for its incredible thermal stability—it can remain stable across a huge range of temperatures, from cryogenic lows (-269°C) to extreme highs (+400°C), where Mylar would melt or become brittle. This is why Kapton, not Mylar, was the primary material for the James Webb Telescope’s sunshield and is used extensively in flexible printed circuits that require high-temperature soldering. Kapton is significantly more expensive than Mylar.

4. How do you seal Mylar bags?
Mylar bags are sealed using heat. The most common and effective method is with an impulse sealer, which uses a quick burst of electricity to heat a wire that clamps down on the bag, melting the inner layers together to create an airtight seal. For home use, a standard household iron on a high setting (with no steam) or even a hair straightening iron can be used. The key is to apply enough heat and pressure to fuse the material without melting all the way through it.

References

• DuPont Teijin Films. (n.d.). Mylar® A PET Polyester Film Technical Data Sheet. Retrieved from https://www.dupont.com/content/dam/dupont/amer/us/en/products/packaging-materials/assets/documents/MYLAR_A.pdf
• NASA. (2021). The Sunshield: Webb’s Sun Hat. James Webb Space Telescope. Retrieved from https://webb.nasa.gov/content/observatory/sunshield.html
• Specialty Tapes. (n.d.). Understanding PET Plastic (Mylar) and its Applications. Retrieved from https://www.specialtytapes.net/blog/understanding-pet-plastic-mylar-and-its-applications/

Disclaimer

The information on this page is for informational purposes only. RM makes no representations or warranties, express or implied, as to the accuracy or completeness of this information. For any third-party services procured through the RM network, it is the buyer’s responsibility to specify and confirm performance parameters, tolerances, materials, and workmanship during the quotation process. For more detailed information, please do not hesitate to contact us.

RM: Your Precision Manufacturing Partner

RM is an industry leader in custom manufacturing solutions. With over 20 years of profound experience, we have become the trusted partner for more than 5,000 clients worldwide. We specialize in a comprehensive range of manufacturing services—including high-precision CNC machining, sheet metal fabrication, 3D printing, injection molding, and metal stamping—to provide you with a true one-stop-shop experience.

Our world-class facility is equipped with over 100 state-of-the-art 5-axis machining centers and operates in strict compliance with the ISO 9001:2015 quality management system. We are dedicated to providing solutions that blend speed, efficiency, and exceptional quality to customers in over 150 countries. From rapid prototyping to large-scale production, we promise delivery in as fast as 24 hours, helping you gain a competitive edge in the market.Choosing RM means selecting an efficient, reliable, and professional manufacturing ally.

Explore our capabilities today by visiting our website: www.rapmaf.com