The blockout fabric, shades and blinds all reduce energy costs by cutting the amount of sunlight and UV rays that enters the room. In addition, they protect furniture and floors from sun damage and fading, which makes these high-cost products more durable.
Fabric for room darkening curtains has improved over the years, from that plastic-feeling polyester you probably remember from hotel curtains, to softer, less static-prone options.
Use blackout curtains, shades or blinds in rooms that get the most sunlight (and be sure to pull them during the hottest parts of the day), and in areas where you want no light penetration, like media rooms.
While blackout curtains, shades and blinds are more costly than non-blackout fabrics, they pay for themselves in energy savings, and in preventing premature aging of your home furnishings and fabrics.