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.

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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.

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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...

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Originally Posted by TMusic

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

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That's easy: mylar thermal blankets. I hear recommendations to people to use these to reflect light all the time. If these didn't reflect heat, they'd be useless for their stated purpose. There's also that stuff that looks like mylar bubble wrap that's used for insulation.

Mylar reflects heat. Therefore, it can create hot spots.

As for aluminum foil, it is an aluminum alloy, not pure aluminum, but it's still at least 93% aluminum. Aluminum doesn't mix well with other metals, so it can't go under that number and still make a useful alloy.

I'm kind of skeptical about using a light meter because light reflects differently off of different surfaces. When lights strikes a surface, one of three things happen. Either it's reflected, transmitted, or absorbed. Metals can't transmit light, so it's either reflected or absorbed. Any light that is absorbed would warm the reflector. I think an ideal experiment would put reflective containers under light and see which one absorbed the most heat.

I'm willing to accept that surface finish has a large impact on reflectivity, since smooth things are shiny. This may be the reason aluminum foil isn't recommended, although it does appear quite shiny. Still, I think it's safe to say the standard answer "aluminum foil is bad because it creates hot spots" isn't really accurate.

Damn dude, you need to smoke a joint.

Don't use a light meter, use a laser thermometer and do a side by side comparison. I would, but I don't have a laser thermometer.

This is getting more interesting by the day. Come on kronik, you can't stop now. Establish an experiment and test the theory.:D

Heh, I may do an experiment if I ever get some free time. I realize it's possible to draw some bad conclusions from what I've said, so I'll try and summarize the facts here:

• Mylar is actually clear, and made from the same type of plastic as 2-liter bottles. The stuff we use is actually "aluminized mylar". Aluminum is deposited on it in order to increase its reflectivity and decrease its gas permeability.
• Pure, polished aluminum is probably the most reflective thing there is, or close to it. Most grow light reflectors are made from polished aluminum. Aluminum, like other metals, reflects infrared radiation as well as light.
• There is no fundamental difference between the way aluminum and aluminized Mylar reflect light. Both depend on the high reflectivity of aluminum.
• Surface finish has a large impact on reflectivity. Aluminum foil is not optimized for reflectivity.
• Aluminum forms a thin layer of aluminum oxide on it upon exposure to air. This may change its reflective properties.

Anyway, I think it's safe to say that first, aluminum metal can be made to be an excellent reflector, and second, aluminum foil is no more likely to create hot spots than aluminized mylar. Actually, if mylar is a better reflector of light, it's probably more likely to create hot spots.

This doesn't actually change much. Mylar is still easier to work with and probably a better reflector than aluminum foil. But it does mean that people using mylar need to watch out for hot spots, and people using white paint are probably the real winners. ;)

just to make you happy, I will turn on my 400-watt HPS lamp, (I'm currently between grows, doing maintenance) and use my Infrared Thermometer (accurate to within .2 degrees + or -), and search for 'hot spots' on my Mylar walls, and report back ... :smokin:

Weedhound and I both screwed around w/ our laser thermometers some,
but never comparing aluminum foil / mylar . Just mylar / flt. wht. pnt. and found there to be about an 11 deg. dif. measuring the temps at the same distance from said surface . Ask real nice and 1 of us might do the same for you guys foil / mylar arguments . :D

Peace
Crispi :jointsmile:

Dejavu huh Reaper ,
Folks need to go drop the 20.00 and buy some neat new toys like the big kids have . :D
Peace bro.
Crispi :jointsmile:

:wtf: ... well, I just now discovered something of importance ... I had heard many times, that Mylar reflectance is affected by it's overall condition (scratches, smudges, etc) ... but, I never knew how much ... my Mylar is (I thought) in pretty nice condition, I clean it only with Windex and soft papertowels ... looks very shiny, not dull, BUT ... the corners of my cabinet are flat-white painted 2x4s ... the walls are all quality Mylar ... my white 2x4s are reflecting twice as much light as my 'one-year old shiny Mylar' ... damn it ... :wtf:

it solved a problem, I'm building a new cabinet soon, but can't afford Mylar (even being a mega-rich drug kingpin :wtf:) ... so, now that I know the Mylar isn't holding up well, I will paint it flat white, like I did for years ... :jointsmile:

Atomik Digital Micro Temp Gun 2 Infrared Traxxas w/Case - (eBay item 220149303684 end time Sep-21-07 20:58:00 PDT)


Real cheap tool that pays for itself quick .

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Originally Posted by the image reaper

it solved a problem, I'm building a new cabinet soon, but can't afford Mylar (even being a mega-rich drug kingpin :wtf:) ... so, now that I know the Mylar isn't holding up well, I will paint it flat white, like I did for years ... :jointsmile:

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Panda, my man...Panda.

'cuz ya can clean it.

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Originally Posted by BeforeYourTime

Holland Hydroponics - Reflective Material

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

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foil causes hotspots and aint recommended for growing cannabis

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Originally Posted by elstonite

foil causes hotspots and aint recommended for growing cannabis

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Wow! WTF?

Someone should make a thread about whether that is actually true or just folk wisdom :wtf:

Grow

I am a pro-commercial photographer and teach advanced lighting classes at 2 universities- here is a photographers opinion based upon 25years of bouncing light- mylar and foil definetly create hot spots with reflected light- if you use foil first wad it up and spread back out- the wrinkles will bounce the light back in all directions- i have found that nothing beats a satin white surface - there is a much more even distributation of the light rays bouncing off this surface where mylar acts as a lens and will focus light rays if the surface is not completely smooth which is near impossible to do-the room I use to start my plants is white

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Originally Posted by rhizome

Panda, my man...Panda.

'cuz ya can clean it.

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the Panda has advantages, for sure, but I don't need much, and can only find it in large, expensive rolls ($75 or so) ... I've always wondered why the Panda works well, as it seems to be a 'high-gloss' white which usually doesn't reflect as well as 'flat-white' ... either way, $$$-wise, I will have to go with flat-white paint again (I don't clean it, I just throw a fresh coat on, every new crop) ... no more easily-scratched and fogged Mylar for me, ain't easy living on Social Security these days ... :smokin:

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Originally Posted by BeforeYourTime

Holland Hydroponics - Reflective Material

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

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Originally Posted by elstonite

foil causes hotspots and aint recommended for growing cannabis

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Here's the thing: every source I can find that claims aluminum foil is less than 50% reflectivity is inevitably linked to the cannabis-growing community. This leads me to believe there is a pot-growing book out there with misinformation in it about aluminum foil.

Apparently, there is a group out there called the "European Aluminum Foil Association" that knows everything there is to know about aluminum foil. Must be a boring group of folks, but they do know foil! Anyway, here is what they say:

"[Aluminum foil] reflects approximately 98% of radiant heat and light. There is no difference between the reflectivity of a bright and a matte foil surface."

source: alufoil - European Aluminium Foil Association

Yes, I have a lot of free time at work. I told my boss yesterday that I don't have much to do and that he should find me more work but he hasn't yet. :D

The European Aluminum Foil Association---who'da thunk it?---lol

Khronik, now since you have so much time on your hands, you could be the first to create the American Association of Solaristics. he he

Seriously though, your prolly right. It prolly started with someone's writing a guess in a book instead of researching to find verifiable fact.

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Originally Posted by ProGroWannabe

The European Aluminum Foil Association---who'da thunk it?---lol

Khronik, now since you have so much time on your hands, you could be the first to create the American Association of Solaristics. he he

Seriously though, your prolly right. It prolly started with someone's writing a guess in a book instead of researching to find verifiable fact.

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I think you mean "American Society of Solaristics." ;)

I want the title "Marijuana Mythbuster". :D Coming up next, khronik tests the myth that cannabis plants are unharmed by the detonation of massive quantities of plastic explosives!

xcrispi, thanks for the info. I had no idea that those thermometers were so cheap now.

yup, like most electronics, the prices drop fast after awhile ... my Raytek set me back $175 a few years ago, I just now saw an ad selling them for $79 ... figures ... :jointsmile:

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Originally Posted by ProGroWannabe

Khronik, now since you have so much time on your hands, you could be the first to create the American Association of Solaristics. he he

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:wtf:

And to think I call myself one of those who proof-reads what I type. Oh well, gotta stick my foot in my mouth every now and then I guess:D.

And yeah guys, I hate when the price drops hard AFTER I had to have something--and paid the original price for it.

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Originally Posted by ProGroWannabe

And yeah guys, I hate when the price drops hard AFTER I had to have something--and paid the original price for it.

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Seems like that happens to most things I buy. Oh well, you can wait a few years and buy it when it's about obsolete, or have it now.

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Originally Posted by Opie Yutts

xcrispi, thanks for the info. I had no idea that those thermometers were so cheap now.

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No problem man ,
My buddy races r/c nitro pwrd cars and uses 1 to tune motors via. cylinder head temps . I got tired of borrowing his .

Our Sis. Weedhound is the one that deserves credit for this , her H/G turned her on to using them in the growroom . Im just the tight ass that found them for cheap . :D

:thumbsup: on the info I've seen you handing out on the site BTW .
Peace bro.
Crispi :jointsmile:

Use elastomeric white roofing paint. IT is just like flat white paint with a kick. IT usually rates around 90% reflective. It's almost mold resistant and water proof. Most people haven't heard of it. Yet, it's probably the best solution. They sell it at most at Homedepot, Osh and Lowes.