Reflectance is not the same as reflectivity. White paint has very high reflectance, while a mirror has very high reflectivity(technically defined by how close it is to mirror image), and very high reflectance(the sum of all reflected radiance, diffuse or specular, it sometimes even includes the emissivity caused by incident light).
Foylon is laminated aluminum foil. How is a plastic coating over aluminum going to help reflectivity? It's not, it hurts it. Aluminum doesn't reflect more than 92% of visible light. It's not physically possible for aluminum alone to do this, you'd have to coat it with magnesium fluoride or some other fluorescent coating to achieve over 92% in the visible region of light.
Cleaning aluminized Mylar?! You've obviously never dealt with this material. Talk about an exercise in futility. It's flimsy as all hell. Good luck if you can even get it hung flat, something, uh, I don't think I've ever seen. Usually it's wavey or otherwise distorted('hot spots' and uneven reflection), even if you managed to apply it correctly, it'll likely not be that way for long unless you get the real thick aluminized Mylar where the aluminum holds it together better. And if you clean it?! Impossible to keep it mint. Foil? You could throw it away, it's cheap.
You'd have to be a moron to crinkle up aluminum foil to the point it becomes a 'light waster'. It's really simple, apply glue to a surface evenly, take the foil OUT of the carton it comes in, unroll it, DO NOT use the stupid cutter on the carton, use scissors. Use a soft clothe to smooth it out nicely bonding it to the surface with the glue. Viola. Nearly perfect piece of nearly pure aluminum.
Mylar does have as much as 2x the ability to specularly(mirror-like) reflect light as does aluminum foil. And aluminum foil has as much as 2x the ability to specularly reflect light as does white paint.
Yes, white paint more 'evenly' diffuses light. They even make white paints with as much or even slightly more reflectance than aluminum foil. The light it does reflect off the surface is less intense, though, as it's not as specular as foil, and is two times as diffuse(nearly 100%). The throw/penetration of the light is most substantially lowered by this difference. Making white walls very unideal for reflecting back USABLE light by the time it hits the plant(s). Very good for the relatively low light humans find comfortable. White paint is for humans, aluminum surfaces are best for plants which thrive under much more intense light than us humans find comfortable. Aluminum lighting sheet is the absolute best material for this purpose. Aluminized Mylar is also very good though, as is aluminum foil(which side DOES NOT matter significantly -it's negligible).
But really, do the measurements, if the distance from the bulb to the wall, back to the plant is greater than the ideal range of the bulb... you're wasting your time. Get more bulbs, or higher wattage bulbs. You'll be much better off.
Oh, and then there's:
https://www.rollitup.org/toke-n-talk/78536-jorge-cervantes-big-fat-idiot.html
