Blackout curtains are heavy, opaque curtains that are designed to block out most or all of the light coming through a window. They are often used in bedrooms to create a dark environment for sleeping, or in media rooms to improve the viewing experience. Blackout curtains can also help to reduce heat loss from windows in the winter, and keep rooms cool in the summer by blocking out the sun's rays. They are typically made of thick, heavily woven fabric, and may be lined with an additional layer of material to block out even more light. Some blackout curtains in coventry also have a thermal coating to help insulate the room and reduce energy bills.