The best blackout materials for light deprivation are durable, UV-resistant, and completely opaque to block out all light. Typically, multi-layered polyethylene films are used because they are both lightweight and highly effective at preventing any light penetration.
These materials often feature a reflective white outer layer, which helps to reflect sunlight and reduce heat buildup, and a black inner layer to ensure total darkness inside the greenhouse. The materials should also be waterproof and resistant to tearing or wear to withstand outdoor conditions and repeated use.
