Silica aerogels are 97 percent porous, meaning light moves through the material but the interconnecting nanolayers of silicon dioxide trap infrared radiation and greatly slow the conduction of heat. A thin translucent layer of low-thermal-conductivity material also blocks UV, directly replicating the radiative effects of Earth’s atmosphere.
The researchers behind this new study used models and experiments to show that a thin, 2 to 3 cm (.8 to 1.2 inch) layer of aerogel could allow sunlight to penetrate, but would trap heat.
My question is, what is the reason that UV light gets blocked, but infrared light doesn't? Is there a reason for this? And why/how does infrared get trapped? I assume silica aerogel is able to heat a surface, because infrared gets trapped and can't escape because of the low thermal conductivity, but why doesn't the infrared get blocked in the first place, like UV? Why would it block longer wavelengths but not shorter ones?