Wait a second... first it was foil burned plants because it dimples and now it burns plants because it's flat?
Mylar is flat and more reflective than foil!! AHhhhHHHhHHH! One time a mylar wall burnt down my house and then the super bright beam hit a plane and caught it on fire and then hit a satelite and burnt it up!! AhhhHHhhhHH!!
You guys crack me up. FOIL CANNOT BURN PLANTS or anything else any more than mylar, polish aluminum, white pain... Way too funny. Read a physics book. This has got to be the silliest rumor of them all as I guarantee you no one has ever seen a plant burned by aluminum foil. The generally accepted ranking of reflective surfaces is thus - Polished aluminum, closely backed mylar, aluminum foil, white paint. This is the generally accepted ranking based on many many light related forums (indoor gardening, aquarium... not just RIU) If polished aluminum is more reflective than foil then why would a dimple in polished aluminum not burn a plant? Why wouldn't a dimple in mylar burn a plant?
The thought behind foil burning plants is that it wrinkles easily and that a tiny tiny wrinkle can focus enough reflected heat that the heat burns the plant. So if you take the same small wrinkle in foil and create it in mylar (which reflects more heat than foil) then the mylar would burn the plant even more - same applies to polished aluminum. I keep my dimpled polished aluminum reflector 4" from my plants... Wouldn't a dimple ~6" from my plant and 2" from my bulb focus more light than a dimple in foil several feet from the bulb? Why doesn't my light burn all of my plants? This is super super simple people. Hell mylar creates large parabolic dimples more often than foil - a larger parabolic dimple in mylar would reflect far far more heat onto a single small spot than foil could ever accomplish.
I personally created a large parabolic dish out of foil in attempts to burn a plant and had no success. With a large enough mylar dish though... that's some heat.
The argument that it is dangerous because it is flat is even crazier. Light reflects at an equal and opposite angle off of flat surfaces. There is no way a flat surface is ever going to concentrate enough light onto one point to create a heat build up. This is like elementary school stuff...