dude, mylar and plastic are cheap, i got a 25'x5' roll for 30 bucks, if your growing small space you can have enough to change it out as needed, as mylar gets wet it looses its reflect ability. white plastic is 1.19 per foot, and its folded to be 10 ft tall so if your really that cheap your probably growing with cfls, which don't get as hot, but still id go with better reflective materials.. mirrors arent any good eather, and XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX