Mylar vs. foil

For a long time I assumed everyone knew what they were talking about when they said not to use aluminum foil, and to use mylar. Apparently foil can create hot spots. But here's the thing, so can mylar. In fact, it's often used precisely because of its ability to reflect heat!

Anyway, I've heard all sorts of misinformation, like that aluminum foil is only 40% reflective whereas mylar is 98% reflective. So I looked up some data in my thermodynamics textbook from college. Actually, polished aluminum is MORE reflective than mylar! Most mylar has a bit of transparency to it, whereas aluminum is completely opaque. And here's the kicker: mylar is made reflective by depositing aluminum on it!

Aluminum is used because it has a reflectivity of 92-98% depending on the wavelength of the light. Granted, aluminum foil isn't the same as pure aluminum, and isn't optimized for reflectivity, but still, according to its thermodynamic properties, there is NO difference between the way aluminum and mylar reflect light. The only difference seems to be that mylar is much easier to work with, which admittedly, is a major advantage.

So here's my question: is there a reason you guys say not to use foil, or are you just repeating what others have said?

Muy interesante...

You would think, however, that the Men with Photometers would have tested it. Or perhaps it speaks to the difference between the ideal aluminum surface described in your book and the aluminum foil available everywhere.

But golly gee, if I could go to Mom and Pop Shop and buy 92-98% reflectivity... !

I used foil...dull side out...no problems. Next time... flat white paint.

Holland Hydroponics - Reflective Material

Foil may reflect more heat but mylar wins hands down on light reflectivity.

nice argument, but just doesn't hold up ... Mylar IS much more reflective than foil (and, the 'transparency' of it doesn't matter, as it is normally placed upon a wall, or sheet of plywood, etc.) ... and I know this, by measuring the reflected light with my light meter (hand-held photographers spot-meter) ... flat white is second place behind Mylar, foil is WAY down the list ... :smokin:

i prefer not to foil or use mylar and just rely on the matte white paint....yea its not quite as reflective but there's no hot spots!

Oh gee I can't stay out anymore. Time to give my two cents, I'm feeling analytical tonight.

The way I "see" it --lol--we're comparing apples to oranges, for most practical purposes. Khronik stated that aluminum in it's nearly pure form, has a high reflectivity. I can buy that. Polish it, the reflectivity goes up. I can buy that too. However, when we say "foil" it all goes to h#ll in a hand basket, like Goldenass briefly touched on.

Why? Because foil is an alloy, for one. But just as important, is the fact that the surface texture of foil compared to that of mylar, is VERY different. Put them under a microscope and just analyze it visually. Thirty power should do it.

Personally, I think the reflectivity of a given material is mostly in it's surface texture. A point can be made regarding how far into a material, that the light beam travels, before being reflected. A mirror appears to be a good reflector to the naked eye. But we all know better. Why, because the light beam has to actually travel through the glass, before it hits the actual "reflector" on the back side of that glass. Then, it has to travel back through the same thickness of glass again, before it reaches a plant to be absorbed. Common knowledge for the posters above me, sure, but maybe someone else can use the info.

As far as I know, IR has done the true test with a verifiable light meter, in the proper environment no less. So, I guess the proof is in the pudding.

Quote:

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Originally Posted by khronik

For a long time I assumed everyone knew what they were talking about when they said not to use aluminum foil, and to use mylar. Apparently foil can create hot spots. But here's the thing, so can mylar. In fact, it's often used precisely because of its ability to reflect heat!

Anyway, I've heard all sorts of misinformation, like that aluminum foil is only 40% reflective whereas mylar is 98% reflective. So I looked up some data in my thermodynamics textbook from college. Actually, polished aluminum is MORE reflective than mylar! Most mylar has a bit of transparency to it, whereas aluminum is completely opaque. And here's the kicker: mylar is made reflective by depositing aluminum on it!

Aluminum is used because it has a reflectivity of 92-98% depending on the wavelength of the light. Granted, aluminum foil isn't the same as pure aluminum, and isn't optimized for reflectivity, but still, according to its thermodynamic properties, there is NO difference between the way aluminum and mylar reflect light. The only difference seems to be that mylar is much easier to work with, which admittedly, is a major advantage.

So here's my question: is there a reason you guys say not to use foil, or are you just repeating what others have said?

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seems like you rebutted your own argument. Aluminum foil is NOT polished aluminum (so why are you quoting this???), and is not optimized for reflectivity. So there IS a difference in the "way" aluminum foil reflects light and the way mylar reflects light.

Who's making walls out of polished aluminum??? That's what someone would have to do to test your ...ummm... "theory"...

There a many more people who have a problem keeping heat down in their growing area than the latter. Mylar instead of foil certainly wouldn't hurt this kind of situation.

Now I have a question. Are you trying to make a point or are you just repeating what other people who don't use mylar say (only a trying to sound a little smarter)?

Just for kicks...

I'd also like an example of an application of mylar "precisely because of its ability to reflect heat!"...

He was asking if people just keep shouting the same age old theory that mylar is way better than foil for reflective purposes, or is there truth in the statement.

Also. the "example" you asked for in the bottom of your post about heat reflectivity---think infrared detection equipment. They woould not be trying to "keep heat" inside the room, just keep it from being visible to IR detection.

Quote:

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Originally Posted by ProGroWannabe

A He was asking if people just keep shouting the same age old theory that mylar is way better than foil for reflective purposes, or is there truth in the statement.

B Also. the "example" you asked for in the bottom of your post about heat reflectivity---think infrared detection equipment. They woould not be trying to "keep heat" inside the room, just keep it from being visible to IR detection.

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A. He didn't really ask a question... he attempted to make an educated argument and breezed over the most important fact. Then he pretended to ask a question.

B. I don't understand that...