Mylar is a reflective wall covering used to direct unused light back to the growing space. A good indoor grower knows that this is an inexpensive way to boost the efficiency of costly lighting systems. 2 mil grade Mylar is the most durable available; choose from 25, 50, and 100 feet. Simply affix to a flat surface using thumb tacks, tape, or staples. All rolls are 4 feet wide.