Blackout curtains are specially designed window coverings that block out external light and provide a darkened environment in a room. Neutral blackout curtains are typically made from thick, light-blocking materials that prevent sunlight and artificial light from entering, thus creating darkness even during the daytime. 

This light reduction can be particularly beneficial for promoting the production of melatonin, a hormone essential for regulating sleep-wake cycles. By blocking light, blackout curtains help improve sleep quality, making them a popular choice for bedrooms and areas where light control is crucial for a good night's sleep and overall health.