Insulating glass, also called insulated glass, are sealed units. It refers to two or more lites of glass glazed along the edges with spacers. The composed glass could be monolithic, or laminated glass, with or without coatings (low e coating as typical). There are types of spacers available, such as stainless steel, aluminum, warm edge spacers in various colors. The space between the glass is sometimes filled with noble gas, such as argon or krypton. 90% filled, which is more helpful to reduce energy consuming. The most common architectural insulating glass unit configuration is 1/4" glass, 1/2" air space and 1/4" glass.

Commonly referred to as an "IGU," insulating glass is the most effective way to reduce air-to-air heat transfer through the glazing. When used in conjunction with low-E or reflective glass coatings, IGUs become an effective means to save energy.