  Thermal management is ubiquitous in the modern world and indispensable for a
sustainable future. Radiative heat management provides unique advantages
because the heat transfer can be controlled by the surface. However, different
surface emissivities require different tuning strategies. Here, we demonstrate
a triple-mode mid-infrared modulator that can switch between passive heating
and cooling suitable for all types of object surface emissivities. The device
is composed of a surface-textured infrared-semi-transparent elastomer coated
with a metallic back reflector, which is biaxially strained to sequentially
achieve three fundamental modes: emission, reflection, and transmission. By
analyzing and optimizing the coupling between optical and mechanical
properties, we achieve a performance of emittance contrast = 0.58,
transmittance contrast = 0.49, and reflectance contrast = 0.39. The device can
provide a new design paradigm of radiation heat regulation to develop the next
generation wearable devices, robotics, and camouflage technology.
