Not many people have seen apartment doors with glass windows, because we do not want everyone to be able to take a look at our private lives. However, excluding this particular instance, doors are often used to create only notional boundaries between rooms, not to conceal things or to keep people out. A glass door can be partially transparent or even opaque, but it would still create a much lighter and airier impression than doors of some other material. A transparent glass door creates a sense of openness and reliability, while protecting you from outside noise. A partially transparent glass door (e.g., toned or silk-screen printed glass) increases privacy without the feeling of being confined. Behind an opaque glass door, people can do what they like without having to worry about unwanted glances, but even such a door would be a supreme design element.