I use reflective radiant barrier from lowes in 3 of my rooms ( clone, veg and flower). The rooms "appear" to be brighter but without a light meter, I can't do a comparison. I've used mylar and won't use it again. Too much of a pain in the ass. Dulls too easy. The radiant barrier needs to be cleaned occasionally but won't dull out like the mylar. Just use spray glue to apply the barrier to your walls. Works good to reflect heat from reservoirs and tubing, too. Make sure not to have ANY air spaces between the walls and the barrier. It will heat up and moisture can form behind it. About $50 for a 25' x 4' roll at Lowes. You can get it much cheaper online if you look around. My original purpose for getting it was for peace of mind with FLIR. Honestly, not sure if it works for that or not. My room is completely lined and sealed to prevent heat signatures. Of course, lining the entire room increased the temps a bit. If you're already having heat issues, adding mylar or radiant barrier could make it worse. The simplest way is paint. Nothing wrong with it at all. My new flower room is painted with white exterior elastomeric paint. It's really thick and easy to apply. Seals up spaces and cracks if you have them. The paint itself doesn't look like it's super bright white so i'm gonna look into what JK uses.
