Penn Engineers Stack Hundreds of Mylar Sheets Into a Tough Insulator for Moon Bases

Engineers at the University of Pennsylvania say the key to keeping a moon base warm may be the same plastic that wraps runners after a marathon. They have built a stack of hundreds of thin Mylar sheets that insulates well in a vacuum and, unusually, survives being squeezed and bent.

Lunar temperatures swing from hundreds of degrees below zero to boiling, so insulation is essential for any long-term presence there. But many of the best insulators are not built for the bumps, compression and repeated handling that construction and maintenance on the moon would involve. Aerogels, which are made largely of empty space, are excellent insulators used on pipelines and NASA's Mars rovers, but they are fragile. Multilayer insulation, a staple of spacecraft, uses reflective films separated by spacers. It is very good at blocking radiated heat but cannot bear much load and tears easily when touched.

That creates a trade-off in which making an insulator tougher usually makes it a worse insulator. "For lunar infrastructure, we would ideally like both," said Igor Bargatin, an associate professor of mechanical engineering and applied mechanics at Penn and senior author of the study. "The ideal material is both resistant to damage and to the loss of heat."

The team started with Mylar, formally known as biaxially oriented polyethylene terephthalate, a polymer already common in aerospace. Coated with aluminum, it blocks infrared radiation and traps heat, which is why it appears in emergency blankets. The researchers tested films of several thicknesses, coated some with an extremely thin layer of aluminum oxide to stiffen them, and stacked them one sheet at a time. They call the result hybrid layered insulating film stacks, or HyLIFS, and describe it in the journal ACS Applied Materials & Interfaces.

Tested in a vacuum, the stacks combined strong thermal insulation with mechanical durability, two properties that rarely appear together. "These stacks of Mylar can bend, withstand substantial compression and maintain their insulating performance," Bargatin said, "potentially allowing them to be packed, transported and survive rough treatment over many years of use."

First author Danielle R. Levin, a recent Penn doctoral graduate in chemistry who also earned a master's in mechanical engineering, said the combination of thermal and mechanical robustness is critical for long-term lunar use. "This material could open a pathway to inexpensive, durable and reusable lunar insulation," she said.

Making it is still slow. "At the moment, the process is very time-consuming," Levin said. "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." If the technique can scale from the lab to mass production, the researchers say it could serve lunar habitats, spacesuits and other equipment that must work for long periods in the vacuum of space.