Block out curtains are designed to block out the light when they are fully closed. Block out curtains are made from a very heavy, tightly woven fabric, but they are more commonly made by lining a curtain fabric with a heavy backing that light cannot penetrate through.
Blockout or lined curtains are Ideal for bedrooms when you want to obtain complete darkness for a good night's sleep.
Blockout curtains have thermal properties they keep the warmth in the house during winter by providing a barrier between the colder outside and the warmer inside preventing heat transfer. In summer Blockout Curtains have an acrylic white foam coating on the reverse or on the reverse of the lining fabric if the curtains are lined, this white coating also helps to reflect the sun during the summer and prevent heat absorption into the fabric and then transferring the heat inside.