Did you know that clear glass transmits up to 90% of solar radiation. It either absorbs or reflects only 10% of solar radiation.You would think since clear glass can transmit solar radiation in, it can also transmit it back. The beauty is that, it doesn’t, after solar radiation is transmitted through the glass and absorbed by the home, it is radiated again from the interior surfaces as infrared radiation.
Although glass allows solar radiation to pass through, it absorbs the infrared radiation. The glass then radiates part of that heat back to the home’s interior. In this way, glass traps solar heat entering the home. So that’s why many energy efficient homes have almost all glass walls or large windows.
Source: http://www.energysavers.gov