Establishing a long-term human presence on the Moon will require materials capable of withstanding extreme environmental conditions. Lunar temperatures can fluctuate from hundreds of degrees below zero to boiling, making effective insulation essential for protecting habitats and equipment. However, many high-performance insulating materials are fragile and struggle to withstand compression, impacts and repeated handling.
Engineers at the University of Pennsylvania (Penn) are exploring a potential solution using hundreds of thin sheets of Mylar, the lightweight plastic used in household food wrap and, when coated with aluminium, reflective emergency blankets that help runners conserve body heat.
In a new paper published in ACS Applied Materials & Interfaces, the team describes a method for assembling these sheets into a material called hybrid layered insulating film stacks (HyLIFS). The material combines two properties that rarely occur together: strong thermal insulation and mechanical durability.
“These stacks of Mylar can bend, withstand substantial compression and maintain their insulating performance,” says senior author Igor Bargatin, Associate Professor in Mechanical Engineering and Applied Mechanics (MEAM), “potentially allowing them to be packed, transported and survive rough treatment over many years of use.”
If the technology can be scaled from laboratory samples to mass production, it could provide insulation for lunar habitats, spacesuits and other technologies designed to operate for extended periods in the vacuum of space.
“The combination of thermal and mechanical robustness is critical for long-term use on the moon,” notes first author Danielle R. Levin, a recent Penn doctoral graduate in chemistry, who also received a master’s in MEAM. “This material could open a pathway to inexpensive, durable and reusable lunar insulation.”
Why Conventional Insulation Materials Fall Short
Designing insulation for a vacuum requires more than simply preventing heat from moving through a material. The insulation must also withstand the mechanical demands of construction, transportation and long-term use.
Some of today’s best-performing insulation materials are extremely fragile. Aerogels, for example, are lightweight materials composed largely of empty space. Their structure makes them excellent insulators for applications ranging from industrial pipelines to NASA’s Mars rovers, but can also leave them vulnerable to mechanical damage.
Multilayer insulation, another technology commonly used in space, relies on reflective films separated by insulating spacers. Although highly effective at limiting heat transfer through radiation, it is not designed to bear significant loads and can tear easily when touched.
These limitations create a fundamental trade-off: improving an insulator’s mechanical strength can compromise its thermal performance.
“For lunar infrastructure, we would ideally like both,” says Bargatin. “The ideal material is both resistant to damage and to the loss of heat.”
The Penn team sought to overcome this challenge by developing an insulating material that could retain its thermal performance while withstanding compression and physical handling.
How Stacked Mylar Films Provide Thermal Insulation
The researchers used Mylar, formally known as biaxially oriented polyethylene terephthalate (BoPET), a polymer already widely used in aerospace applications and in emergency blankets given to marathon runners. When combined with a metal such as aluminium, Mylar can block infrared radiation and help trap heat.
The team tested films of different thicknesses, coating some with an extremely thin layer of aluminium oxide, also known as alumina, to increase their stiffness. The researchers then stacked the films one sheet at a time.
“At the moment, the process is very time-consuming,” says Levin. “We use two pairs of tweezers and small weights to handle and stack the delicate films. Even breathing near the stack can send the layers flying.”
Despite the delicate manufacturing process, the resulting material demonstrated a promising combination of thermal and mechanical properties.
Tests conducted in a vacuum showed that the best-performing stacks achieved thermal conductivity comparable to other high-performance vacuum insulation technologies when compressed under conditions resembling those in a lunar habitat with air maintained at atmospheric pressure indoors. The material also remained flexible.
In separate mechanical tests, the coated stacks maintained their thermal performance even under the highest compressive stresses achievable with the laboratory’s equipment. The results suggest that the material can provide effective insulation without sacrificing durability.
Mylar Insulation Withstands Repeated Compression
The researchers were surprised by how well the material performed under substantial mechanical stress.
The team repeatedly compressed samples to approximately 20 megapascals, roughly equivalent to concentrating 200 pounds onto the area of a fingertip. The experiments tested whether the layered films could withstand repeated compression without losing their insulating properties.
“We were concerned about the material failing under such high compressive stress,” recalls Levin. “But the stacks didn’t survive just one high stress cycle — they survived 10 in a row.”
This durability could offer practical advantages for lunar construction. Materials transported to the Moon must withstand the journey before being installed, while equipment used in lunar habitats may experience accidental impacts and repeated handling.
“You could use these stacks to insulate a lunar habitation, but astronauts will inevitably have little accidents where they bump into them,” notes Bargatin. “When we’re talking about long-term habitation on the moon, it’s really important to have tough materials that can last long enough.”
A flexible, reusable insulator could therefore help reduce the risk of damage during transportation, installation and everyday use.
Tiny Particles Could Hold the Key to Better Insulation
The study also identified a potentially important role played by microscopic particles already present in commercial Mylar films.
Extremely thin plastic films tend to cling to themselves and other surfaces, making them difficult to manufacture and handle. To prevent this, manufacturers add microscopic particles known as “antiblocking” particles. These protrude slightly from the film’s surface, preventing adjacent layers from sticking together.
Although the particles and their industrial purpose were already known, their influence on heat transfer through stacked Mylar films had received relatively little attention.
Conventional multilayer insulation primarily aims to limit heat transfer through radiation. As a result, there has been less reason to investigate whether these microscopic particles create pathways for conductive heat transfer between adjacent sheets.
To examine this possibility, the researchers developed models of heat transfer across the interfaces between films and compared their predictions with experimental data. Their results suggest that, in a vacuum, heat primarily travels between sheets at the microscopic points where antiblocking particles touch neighbouring films.
This finding could help researchers design more effective insulating materials. Rather than treating the particles as an unavoidable feature of commercial Mylar, engineers could potentially adjust their size, number and distribution to control heat transfer.
Why Thinner Films Do Not Always Provide Better Insulation
The researchers also discovered that thinner films do not necessarily produce better insulation.
Initially, the team expected the thinnest films to perform best because thinner sheets allow more layers, and therefore more interfaces that limit heat transfer, to fit within the same space.
However, the thinnest successfully characterised films and those of medium thickness performed similarly when coated with alumina.
The researchers believe the antiblocking particles help explain this result. In thinner films, these particles can create more contact between neighbouring layers, opening additional pathways for heat to flow through the material.
“As you compress the layers the contact landscape changes,” says Levin. “It’s not just a matter of minimizing the film thickness or the number of particles; we must also account for how the contacts change and the films deform as pressure increases.”
The findings indicate that insulation performance depends on several interacting factors, including film thickness, stiffness and the distribution of embedded particles. Optimising the material will therefore require researchers to consider how these characteristics change under pressure rather than simply minimising film thickness.
Scaling Mylar Insulation for Lunar Habitats
For now, the HyLIFS samples remain small, measuring approximately one square centimetre in area. Producing them is also time-consuming, with manual cutting and stacking taking hours.
Practical applications would require insulation sheets measuring metres rather than centimetres. Scaling up production will therefore require a different manufacturing approach.
The researchers point to techniques such as continuously coating large rolls of Mylar as possible ways to manufacture the material at a larger scale. In the future, engineers could adjust film thickness, coatings and antiblocking particle distribution before winding the material into large stacks.
However, important questions remain about how the material will perform at larger scales. Further testing will need to establish whether the films can withstand repeated bending, bumps and scuffs under real-world operating conditions.
If the material retains its promising small-scale properties when manufactured at larger sizes, it could eventually serve as flexible insulation for lunar habitats, rovers, electronic systems and other equipment used in space.
For Levin, the research also demonstrates the potential of revisiting familiar materials to discover new applications. “The simplest configuration ended up being the best one,” she says.
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