For large, wide windows and sliding glass doors, vertical blinds are an excellent window covering option. Vertical blinds come in a variety of treatment types including metal, vinyl, fabric, wood, and cellular blinds. For sliding patio doors, vertical blinds provide easy access and exit as well as a number of light filtering options. A simple twist of the wand varies the natural light filtered in by the degree to which the blinds tilt. Vertical blinds are fully adjustable to protect a room from harsh summer sun when fully closed. Cellular blinds actually promote energy efficiency in all seasons as they trap air in a pocket, creating a layer of insulation.