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May 31, 2006

Why does aluminum foil have one shiny side and one with a matte finish?


Ever think about that?

And wonder which side should face the food?

Robert L. Wolke, in his "Food 101" column in the May 24 Washington Post Food section, explains it all for us.

Here's what he wrote:

    First, a brief bit of history.

    In the 19th century, Thomas Edison invented a phonograph machine, in which a sound-driven vibrating needle impressed grooves into a cylinder covered with a thin foil of the soft metal, tin.

    In the 20th century, tinfoil was being widely used as a wrapping material for foods and drugs.

    By the middle of the century, tinfoil had been replaced almost completely by thin foils of a different metal called aluminum.

    Yet many people persist in calling aluminum foil "tinfoil."

    We chemists get annoyed at things like that.

    Get with it, folks!

    This is the 21st century!

    Now, about aluminum foil.

    Aluminum foil is made by rolling sheets of 98.5 percent pure aluminum metal between pairs of polished, lubricated steel rollers.

    Successive passes through the rollers squeeze the foil thinner.

    Household aluminum foil is so thin (0.0005 of an inch) that the rollers can't handle it without tearing it.

    The final rolling is therefore done on a sandwich of two sheets, face to face.

    The outer surfaces emerge with a finish as smooth as the rollers, while the two face-to-face inner surfaces emerge with a matte finish.

    Hence, a shiny side and a duller side.

    When you use the foil, it makes no difference which side is up, down or sideways.


FunFact (from the same column, different question): "Aluminum is the most abundant metal in the Earth's crust."

Last year a group of researchers from MIT published the results of perhaps the most rigorous study ever performed to investigate whether aluminum foil helmets serve as a protective measure against invasive radio signals.



one of the investigators.

At the very bottom of the MIT site there's a link to an informative video if you'd prefer something visual.

May 31, 2006 at 10:01 AM | Permalink


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It's because there is steam that condenses on the foil above the spaghetti that then drips back down leaving rings on the foil where it dripped off.

Posted by: anonymous | Jul 17, 2009 1:38:14 PM

One of the oldie TV cartoon shows (I'm pretty sure it was the great "Rocky and Bullwinkle") had a running gag about a planet named Muni-Mula, which is, of course, aluminum spelled backward. Maybe the guy investigating the invasive radio signals is from Muni-Mula. Hokey Smoke!

Posted by: Flutist | May 31, 2006 10:16:54 PM

According to Pat & Betty over at Reynolds, it doesn't matter which side is "up" unless you're using their release foil, in which case thefood goes on the dull (treated) side.

As for the spaghetti sauce spots, it's from natural acids in tomatoes released in the steam and condensing on the foil. It discolors the foil but doesn't harm the food.

Posted by: Al Christensen | May 31, 2006 5:01:53 PM

I tend to favor the shiny side up. Also I do wonder why when you put something like spaghetti sauce under foil the foil turns up with little spots on it? The food doesn't even have to touch the foil and it still does that? Makes me think twice about spaghetti sauce and feeding it to children. Anyways I do think I have too much time on my hands today or I am trying to avoid actual work to even worry about this. SHINY side out...rules!!! =)

Posted by: Rhonda | May 31, 2006 11:10:03 AM

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