Pella (r) Impervia (r) sliding glass windows are composed of extremely robust fiberglass and are built to last for many years. They are also very energy-efficient, so your utility bills will be lower during the winter months. Glass is a clear, brittle material that can appear as flat or curved surfaces. Glass has many uses in our daily lives: from windows and doors to electronic display screens. However, it can be harmful if not handled properly during manufacturing or installation/removal of parts. There are two main types of windows: single-glazed and double-glazed. A single-glazed window has one glass pane and does not have a barrier between the inside and outside environments. So, anything that is visible on one side will be visible on the other. Double-glazed windows have an inner and outer glass panel and serve as a barrier against noise, heat, and moisture. This type of window requires special tools for opening; usually either a screwdriver or pry bar is needed to break off the lock washer that holds the sash in place. It's important to remember that windows can be broken easily by those who do not know how to handle them safely.