Sliding window has two or more sashes that slightly overlap and slide horizontally side to side within the frame. Some of the sliding windows on the market only have one side that slides open. Those are called single sliding windows. Single sliding windows were most commonly installed in condominiums 20, 30, and even 40 years ago. Highly conductive aluminum was the main type of material used in production of these windows. The drawbacks of aluminum are that it conducts cold and contributes to excessive condensation around the edges of the insulated glass unit. Another problem with these windows is inflexible aluminum spacer that can lead to sealant failure, which can cause condensation inside of the insulated glass unit – problem known as “foggy” windows. Fortunately, today you have more choices of materials and configurations. Now, most common sliding window on the market is double sliding window, which means that window has two sashes and you can open either side of the window. This feature comes in very useful if you want good air circulation, particularly in rooms with one window. You can also lift out either sash for easy cleaning. Plus improvements in glass, spacer, and frame technologies made sliding window more beautiful, more energy efficient, and virtually trouble-free.