I don't know for sure but I've heard people say that once wrinkled the foil doesn't reflect as much back. Mylar is a reflective coated plastic film. It tents to be very very reflective. They make those light weight emergency blankets out of mylar. I don't know how well mylar works once it has gottent a bit wrinkled but I've been using it. I was too cheap to buy the fancy stuff from the hydroponics store and just got a few of the emergency blankets from Wal-Mart for under a couple dollars each. I actually found that the cheap ones work a little like window tinting so I could drop a curtain of the emergency blanket to help reflect light back in to the plants but I could still see in through the blanket, I thought it was kinda neat.

There is a good chance that a white surface will be more reflective than dull aluminum foil. I sould think that if the foil is the really shiny reflective stuff that it might be ok.

I haven't personally tried aluminum foil, but I've been warned from knowledgable hydro folks that the shiny side can cause focused 'hotspots' from your lights and burn your plants kind of like the 'magnifying glass under the sun burn ants thing'

Alum foil can be glued to a large piece of cardboard by using aerosol spray-on adhesive. This will not create "hot spots'

dcarch

It was probably me that warned against household aluminium foil. It is too thin and contains tiny holes. Hold it up to a light bulb and you'll be able to see through it. Any light that goes through a reflector is wasted.

You want Mylar, or flat white walls. Aluminum foil will cause hot spots and it doesn't reflect the light evenly. for the cost of the aluminum to cover walls, Mylar is in 4' wide by 25 or 50" lenghts. 20.00 for a 25' roll.

I do realize that this question/thread is from 2007 & it's now 2016, but it's still available so I figured that I'd comment. As far as aluminum foil goes, it really depends on what brand and thickness that you use. In many cases, generic foil IS very thin and flimsy. Name brand, on the other hand, tend to be much thicker and have more of a flat "matte" look, rather than being super shiny. I've yet to ever find any holes in my aluminum foil and doubt that I will, especially when using a certain name brand "Wrap." I have also used flat white printer paper around my plants, which can be put on flat cardboard just like the foil. Personally I have not seen a noticeable difference between either method; as long as your using good quality foil or flat white paper you should not have a problem. Happy Gardening!

I'm using Mylar, but here are some reference values you may find helpful:

http://www.engineeringtoolbox.com/light-material-reflecting-factor-d_1842.html

I did research on this a long time ago and read that the most reflective white pigment is barium sulfate. I actually went through the trouble of precipitating some and adding acrylic emulsion. The "hiding power" of the resulting paint was poor and required many coats. Not worth the effort. I now use aluminized mylar film.

Now, that the OP's questions have been answered, it is okay to hijack the thread.

Do you know why one side of aluminum foil is shinier than the other? It is because two sheets are rolled against each other down to final thickness and the least shiny surfaces are those between the two sheets, i.e., the shinier surfaces are those that made contact with the rolls.