As mentioned above, there are currently no products that can honestly promise a total blackout of the bedroom .This is because light can always seep out somewhere ; above, below, or on the side of a blackout curtain ,between two panels or through the gaps But with that said, there are many tricks to use to achieve as close to total blackout as possible. One of the most obvious pieces of advice is about the choice of fabric. Both color and material are important factors for achieving blackout.
If you are looking for a curtain that allows some light to filter in but still blocks out the strongest light, you should choose dimout-fabric, with approximately 60-80% blackout. But real night owls prefer to blackout-fabric, which has a blackout capability of up to 100%