Completely block out ALL light. Completely trap ALL light in. Exact same material used for popular grow tents. Optimum light return on your plants. Reusable and the most rugged reflective material on the market. Get creative: build your own size room. Staple to 2′ x 4’s with ease. Cut holes for ventilation. Thermal, waterproof, and extremely insulative. Non Toxic will not off-gas or react with light and heat. 5 Mil thick. 100 foot roll x 5′ wide. 93% reflective.