Double-glazed windows consist of two panes of glass separated by a space filled with air or gas, which acts as an insulator. This design helps to reduce heat loss in winter and keeps homes cooler in summer, making them energy-efficient. Additionally, double-glazed windows can help reduce noise from outside, providing a quieter indoor environment. They are commonly used in residential and commercial buildings to improve comfort and lower energy bills, while also enhancing the overall value of a property.