# Mylar melting



## treefish (Oct 10, 2007)

Does anyone know the melting temperature of mylar film? 

I have some 2 mil. mylar. I plan on lining the inside of my hood containing 4 T5HO 24W lamps. It will also be fan ventilated. The mylar will be inserted roughly 2" from the bulbs.

Do I have to worry about it melting or catching fire? I know the T5 high output bulbs get warm. I also tested the mylar with a lighter and it lit up like napalm.

This is quality mylar sold in hydroponics shops. I know it's built to withstand some heat, but how much is too much?


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## Volenti (Oct 12, 2007)

My gut tells me that you will be ok, especially with fan forced ventilation.


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## hoppycalif (Apr 7, 2005)

The reflectors I made in this thread, http://www.aquaticplantcentral.com/...ects/45208-diy-mod-perfecto-10-gal-light.html using that mylar, are still in perfect condition. This is with 15 watt screw in CFL bulbs almost in contact with the reflectors.


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## treefish (Oct 10, 2007)

I hope it will be ok because I plan on doing it anyway.

I have never used T5HOs before. I hear they get pretty hot. I have used the spiral compacts, and they stay somewhat cool except for the ballast end. 

I read that fires have been started from mylar in light fixtures, but no first hand accounts. I'm not sure what caused the fires or if they were even true stories. That's why I figured I'd ask to see if anyone else heard of this.

Btw, nice design hoppy.


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## Cliff Mayes (Jan 29, 2007)

Please post your results.


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## Cliff Mayes (Jan 29, 2007)

My normal reply to someone getting nervous and jerky about me going somewhere is "If I get killed I will call." Your response kind of reminds me of that.

Actually I wouldn't think that a reflector on an aquarium light would start a house fire but more that it might melt or distort the Mylar.

At any rate it would be interesting to hear, good or bad.


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## treefish (Oct 10, 2007)

Cliff Mayes said:


> Please post your results.


Haha sure, I'll let you guys know if my house burns down.
Hopefully that won't happen. I think I'll knock on some wood now.


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## treefish (Oct 10, 2007)

Cliff Mayes said:


> My normal reply to someone getting nervous and jerky about me going somewhere is "If I get killed I will call." Your response kind of reminds me of that.
> 
> Actually I wouldn't think that a reflector on an aquarium light would start a house fire but more that it might melt or distort the Mylar.
> 
> At any rate it would be interesting to hear, good or bad.


I'm not sure you made me feel any better about trying this. Thanks for your interest in my possible house fire... I guess...
I was hoping to hear that somebody else tried this before. I know mylar is a popular alternative reflector choice. There has to be somebody out there using it over T5HOs.


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## dt78 (Apr 23, 2007)

I personally, don't have any experience with using Mylar. Doing a quick search on Mylar I have found out that it is made out of a type of polymer known as a thermoplastic. A thermoplastic is a type of polymer that can be reheated and then remolded over and over again. 

One thing to remember with polymers is that there is a glass transition temperature (Tg), and a melting temperature (Tm). The Tm is the temperature above which the polymer changes to a liquid state, and the Tg is the temperature above which the polymer changes from a rigid glass state (brittle) to a rubbery (elastic) state. If the temperature is raised to a temperature above the Tg, but not the Tm, it could start to move and change shape to fit its new container. Obviously, the father you are above the Tg (closer to Tm), the more elastic it will become. In the case of a hood, it could mean that the Mylar could start to sag down and possibly touch the light if the temperature was high enough. It's also important to note that the Tg can be much, much lower than the Tm. 

From what I was able to find after doing this quick search was that there are multiple types of Mylar which all seem have a different Tg. On one website I found that the maximum service temperature (I don't know if this is Tg or not) ranged from about 250*F to 450*F for the different types they had. On another website, an audio forum actually, it listed the Tg of DuPont Mylar as 80*C, or roughly 176*F. Both of these websites listed the Mylar thickness as only a few microns and not millimeters, so I don't know if it is the same thing used in aquarium hoods. 

I can't promise that these numbers are correct as they came from various websites, and I don't like to believe everything on the internet without verifying it first. Before you use the Mylar, you should verify this data for yourself as I have not properly done so. Having said that, if you can find valid data for the type of Mylar you have, make sure the temperature of the bulb is less than the glass transition temperature and not just the melting point, or at least not too much above it. I would also check on it once in a while until I was certain that nothing is going to happen.

A couple other things you might want to find out are:

1. How hot do T5HO bulbs get?
2. How are you going to put the Mylar in the hood? Glue?
If so:
3. How hot can the glue get before it fails?


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## treefish (Oct 10, 2007)

Very helpful information dt78, thank you. 

I tried to look up the melting temperature of the mylar I'm using (Sunfilm) but haven't been able to come up with anything. I'm assuming it's designed for relatively high temps being that its purpose is for hydroponic/plant care applications. Even if it's on the low side, it probably won't be under 176F.

I was planning on taking temperature readings from my hood before I apply the mylar. I'm not expecting it to get that hot, but researching the actual bulb temperature is probably a good idea.

As for installing the mylar, I haven't quite decided how I want to go about it. High temp glue seems like the most effective method, but I'd rather not have to scrape my hood if I ever or ever have to replace the mylar. I have a few other ideas. I'll decide on that when I'm finished construction. I'll just have to remember and make sure the mylar can never rest on the lamps.


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## hoppycalif (Apr 7, 2005)

You can easily glue mylar to almost anything using spray can adhesive, 3M Super 77 spray adhesive. Just spray it on what you want to attach the mylar to and press the mylar in place. It is probably a good idea to try to glue the mylar with the side having the aluminizing on against the glue - assuming it isn't aluminized on both sides as mine was.


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## treefish (Oct 10, 2007)

I am considering the 3M stuff, but I don't know how easy it will be removing the mylar if I wanted to. It is mirrored on both sides. That might make removal a bit easier, but that probably depends on how the mylar and glue react to heat.


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## ABThermal (Feb 20, 2010)

Mylar is a trade name for Polyester, and melts at 440F or 226C. Silicone rubber adhesives (in caulking tubes at home hardware/home depot/lowes etc are good for temperatures up to 450-500F.

More info about mylar film and heat reflecting materials can be found at http://www.firesleeveandtape.com or http://www.extremeheatprotection.com in the catalog at that site.

Adrian


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## trag (Jan 9, 2008)

I've been using reflective mylar in a T5HO fixture wtih two 36" (39 watt) bulbs for a couple of years now. It hasn't caught fire yet. 

Of course, it's been almost three years since the original poster started this topic and we haven't heard back from him, so maybe his results were different.

I adhered my mylar with 3M HiStrength 95. It is very similar to the 77 product but it has higher temperature tolerance than the Super77. The 95 also appears to be stocked at Home Depot in the paint department. It's a little pricey, but you'll probably only ever need one can.


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