A passive thermal regulation system includes a substrate and a coating. The coating is positioned to encapsulate at least a portion of the substrate. The coating includes a first hydrogel layer and a second hydrogel layer. The first hydrogel layer has a plurality of carbon materials configured to absorb a solar radiation. The second hydrogel layer includes a hydrogel that is different from the first hydrogel layer. The coating, at a first temperature, causes the passive thermal regulation system to passively switch from a solar reflective state to solar absorber state to permit the plurality of carbon materials to absorb the solar radiation. At a second temperature, the coating causes the system to passively switch from the solar absorber state to the solar reflective state where the hydrogel of the second hydrogel layer inhibits the solar radiation from absorption. The second temperature is greater than the first temperature.