The side of the blackout curtain that faces the window is typically the darker or the shinier side. This is designed to effectively block out sunlight and heat, providing a darkened room and temperature control. The lighter or more decorative side of the blackout curtain faces the room interior, complementing the room's aesthetic. The blackout material is usually sandwiched between two layers of fabric, with one side designed to face the window to maximize light absorption and the other side designed to blend with the room's decor. Thus, when installing your blackout curtains, ensure the darker or shinier side is facing the window for optimal performance.