There is really no such thing as “soundproof” glass, though there are glasses that can mitigate sound waves substantially. “Soundproof glass” is made specifically to reduce sound traveling through a window. Soundproof glass may be manufactured with thicker glass, spacers, laminated glass, or any combination thereof. A soundproof window can be installed in front of an existing window to increase noise reduction beyond what the original window offers. Despite the name, soundproof glass does not block sound in its entirety, though some window dealers advertise their wares as able to reduce noise up to 90 or 95 percent.