Architected plates feature geometrical patterns that provide advantageous mechanical properties, such as an enhanced bending stiffness or a reduced tendency to tear. In this talk I will introduce our research group’s multiscale hexagonally patterned corrugated plates, which have nano-scale film thicknesses, micron-scale total heights, and square-centimeter-scale lateral area dimensions. I will first explain how we use these plates in direct thermionic heat-to-electricity generators and show that new corrugation modalities provide several-fold reductions in the plates’ thermal conductivity, leading to greater device efficiency. I will then show that our plates can be tailored to become ultra-reflective membranes for photon-propelled space travel near the speed of light, and explain mechanical guidelines for the design of relativistic light sails.