Also using these in my 4x4 grow closet. I was getting light leaks until I put one of these up. Today I'm adding a 2nd one to separate the room into veg sd & flower sd.I use the heavy blankets used for moving furnature and appliances. works wonders.
@greenkrakzak, try www.harborfreight.com if you don't have a local store. That's where I get these, they run 9 bucks.