When it comes to choosing the reflective material, mylar seems to be the obvious pick. There are other options like using a reflective or high gloss white paint.

Most growers would never suggest using aluminum foil to line the walls. The theory is that wrinkles in foil can cause hot spots in reflectivity. But is that just a myth created by the mylar industry?

“Lets go over the facts and you decide what is the best reflective material for your grow room.

Foil vs. Mylar the pros and cons

Cost:  As mentioned above, foil is supper cheap. If we break down the cost per foot on average as well as average cost per grow.  lets figure out the average size of a closet grow, how much material we will need and total cost.

Cost per foot

• Mylar : $1+
• Aluminum Foil: $0.04

So I check around and also measured my closet. So its fairly safe to say that the average closet size in the US is about 5 square feet. The average wall hight is about eight feet, but depending on your set up we will assume your only going to go about 4′ high and layer the ground as well. Lets roughly say the total space is about 40 square feet.

Total cost per grow

• Mylar: $40
• Aluminum Foil: $1.50

Although the price of foil is real, the cost of Mylar isn’t going to break the bank. Even after shipping costs and taxes, I still wouldn’t mind spending the extra cash on Mylar, If it’s worth it, let’s find out.

Reflectivity:  Good grow lighting can be expensive so getting the most out of your investment is important. Luckily, there is something called LRV, or Light Reflective Value testing. I was able to scratch up some information on this as well as the values for each.

Reflectivity Values

• Mylar: 98% reflective, 2% loss
• Foil: 98% shinny side, 88% dull side

Because there are so many producers of foil, the numbers on foil can vary by up to %10 give or take. The LRV for Mylar on the other hand is fairly constant.

But here is the kicker, The test is preformed by using a wider spectrum than needed for growing as well as the thermodynamic insulation value. So, as far your grow is concerned, there may be no real difference, in fact Mylar may actually be less effective!

What don’t believe me?

Here is a test you can do at home.  Hold up a piece of Mylar to a lamp. You can see some light shine through. Now try it with foil, no light passes through.

Usability: Unlike the past two points, which are not totally clear cut, this is. Mylar hands down is easier to use and reuse. Mylar is flexible, reusable and way more forgiving when compared to foil. This will be evident the on day one.

Foil creases, tears and loses shape right away. This is a major disadvantage and may be reason enough to skip foil.

Foil can only be used once and will need to be replaced often. This might not be an issue because due to the low cost, but it is definitely some thing to consider.

Ceases, tears and bumps, ouch! Here is another reason to skip the foil. I’m sure you have heard of foil creating hot spots or focusing to much light  due to creases or wrinkles. There is a little bit of validity to those claims but it may not be an issue.

If you use foil, if possible try to keep a little more space between it and your plants. You can use Aluminum foil successfully but it will take some getting used to.

Thermodynamics: Heat is a huge problem for closet growers. Besides over heating plants and burning leafs. Heat can reduce over all humidity creating a climate thats will reduce yields.

• Mylar: Insulates heat without absorbing “as” much heat
• Aluminum: Absorbs and retains heat!

Mylar is not only a good for reflecting light, it also reflects and insulates heat. Because of this you may have come across Mylar being used in emergency situations by Paramedics to prevent hypothermia.

“Aluminum on the other hand is mostly used in cooking!”

Metals like aluminum absorb heat. This is a problem that can create an “oven” type effect. Although Mylar uses a small percentage of aluminum, it is insignificant compared to aluminum.

So whats the better for a closet grow?

Honestly, Mylar is the the king of the closet grow. Even though the cost of aluminum foil is so low, growing in small spaces will cause issues. Like restricting your ability to provide the best grow environment.

Major points:

• More clearance is need between aluminum and plants
• Aluminum will cause over heating
• Aluminum is not reusable
• Tears, folds and creases to easily
• Creases in foil will cause hot spots

The choice is yours and if you have some experience growing, aluminum foil may work for you. But being that cost and availability are the only real advantage, I would prefer Mylar.

More on Mylar

Although it is actually the name of a specific product. Today Mylar is used as a blanket term used to describe a category of plastic or polyester film.

There are different types of Mylar with different application. From reflective insulation to anti static sheeting. Another form of Mylar you may be familiar with is used as car window tint.

Sources:

• https://www.thoughtco.com/mylar-polyester-film-608929
• http://www.fsec.ucf.edu/en/research/solarthermal/solar_cooker/documents/reflectivematerialsreport.pdf
• http://boards.cannabis.com/threads/mylar-vs-foil.134005/