Anti-fog sheet structure and helmet

An anti-fog sheet structure comprising:

• a substrate made of a transparent plastic,
• a first synthetic polymer film formed on a first main surface side of the substrate, and
• a second synthetic polymer film formed on a second main surface side of the substrate on an opposite side from a first main surface,
• wherein the first synthetic polymer film has, on its surface, a plurality of first bumps having an equivalent circular area diameter Dp1 in a range of more than 50 nm and less than 500 nm as viewed in a normal direction of the first synthetic polymer film,
• the second synthetic polymer film has, on its surface, a plurality of second bumps having an equivalent circular area diameter Dp2 in a range of more than 20 nm and less than 500 nm as viewed in a normal direction of the second synthetic polymer film,
• the first synthetic polymer film is formed from a cured product of a photocurable resin containing 30 mass % or more of ethoxylated pentaerythritol tetraacrylate,
• the second synthetic polymer film is formed from a cured product of a photocurable resin, and
• the anti-fog sheet structure has anti-fog properties such that a time for a visible light in-line transmittance of the first synthetic polymer film to decrease to 80% of an initial value with the surface of the first synthetic polymer film in contact with saturated water vapor at 50° C. is 90 seconds or longer.