Mirrors & aluminum foil are the worst for reflecting light back for plants. Flat white paint is pretty good in a pinch (glossy paint bounces the light the wrong direction and causes hot spots). Mylar is very reflective but you have to put socks on your hands to apply it because finger prints ruin the reflective capability of the Mylar. You have to be careful not to wrinkle Mylar because that will bounce the light in the wrong direction in every area that is wrinkled. 2 mil Mylar is easier to work with because it is thicker then 1 mil Mylar. Mylar also cannot be washed, if you get it wet foliar feeding it is no good & needs to be replaced. Panda Film is very reflective & inexpensive, Panda film (polyfilm) is not quite as reflective as Mylar but close. It is 6 mil’s thick and is black on 1 side & white on the other side. It is washable and easy to use. Panda Film can also be used to block light from getting through. It does need to be replaced after a couple years because Panda Film starts to become brittle. Dureflect is one of the best reflective materials but it is expensive. Dureflect is washable and wrinkles are easily straightened & it is very easy to use. Dureflect is not completely light proof (some pin holes can be seen with use). Ultra reflective (Ultraflect) is one of the best reflective films but it is not as easily straightened as Dureflect. It is washable and easy to use. No pin holes can be seen with Ultraflect.