Robust Layered Thermal Insulator Film Stacks for Vacuum Applications

There is a need for mechanically robust, thin thermal insulators within lunar infrastructure to achieve a sustained presence on the Moon. Existing solutions, including aerogels, multilayer insulation, and vacuum insulation panels, often fail to meet these criteria because they are mechanically inflexible and may thermally short or structurally fail upon accidental impact. To bridge this gap, we report high-layer density (nominally 80 to 400 layers/mm) alumina-coated biaxially oriented polyethylene terephthalate (BoPET or Mylar) sheet stacks as a model system for mechanically robust, flexible, low-conductivity thermal insulation in vacuum environments, with potential relevance to lunar applications. Our measurements reveal that stacks consisting of single- and double-sided atomic layer deposited alumina-coated 2.5, 5, and 12.5 μm thick BoPET films, have thermal conductivities as low as 2.2 mW m-1 K-1 at 0.1 MPa applied compressive stress and temperatures from 35 to 120 °C. They can withstand much larger compressive stresses (>20 MPa in separate mechanical testing) than aerogels or uncoated layered insulators without significant degradation of mechanical or thermal properties within the studied temperature range. HyLIFS are promising vacuum insulation candidates that combine the mW m-1 K-1-scale thermal conductivity of vacuum aerogels and vacuum insulation packages with much higher mechanical robustness (flexibility and compressive strength). Our thermal modeling indicates that the dominant heat transfer mechanism in vacuum is spot conduction through antiblocking particles embedded in BoPET, with strongest agreement at higher compressive stresses, suggesting pathways by which even lower conductivities could be achieved.