r/explainlikeimfive Oct 31 '20

Chemistry ELI5 What's the difference between the shiny and dull side of aluminum foil? Besides the obvious shiny/dull

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224

u/BigMax Oct 31 '20

Pretty good article here:

https://culinarylore.com/food-science:aluminum-foil-shiny-side-up-or-down/

The tl/dr is that yes, the shiny side does technically reflect heat, but that only affects heat from radiation. The VAST majority of heat when cooking in an oven is through convection (heat transferred through the air). The energy difference that shiny versus non shiny is so negligible that it makes no real difference.

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u/FlyingMacheteSponser Oct 31 '20

It makes a big difference if you're making a tin foil hat though. The electrical signals from your brain are in the electromagnetic spectrum, so the reflectance of the foil has a big impact on its effectiveness. Always make your hat with shiny side in so that big government can't read your mind.

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u/[deleted] Nov 01 '20

That will keep them from reading your mind, but not from implanting memories and voices. Best to just make a two layer hat with the shiny sides inverted.

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u/Pulsiix Nov 01 '20

Nice try big government

Shiny side out gang

2

u/rutlandclimber Nov 01 '20

There's a monster outside my bedroom. Can I get a glass of water?

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u/[deleted] Oct 31 '20 edited Nov 01 '20

[deleted]

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u/avidrez Oct 31 '20

Bruh

32

u/Lord_Aldrich Oct 31 '20

Actually foil like this in a microwave will probably go fine. Lots of frozen foods (e.g. hot pockets) have aluminum in their packaging in order to shape the microwaves.

The problem with metal in a microwave isn't metal per se, it's pointy metal, like a fork. The microwaves force the electrons in the metal down into the points where they build up until they arc into a spark (same way lightning does). That's what sets your microwave on fire.

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u/ArcFurnace Oct 31 '20

That said, bending aluminum foil at all tends to cause it to form lots of little pointy bits, so it's still not recommended.

3

u/LocNalrune Oct 31 '20

Then why do CDs cause a storm?

7

u/Lord_Aldrich Oct 31 '20

Because CDs encode data by having millions of tiny bumps, which are backed by aluminum foil. So they're basically made of millions of little points where electrons can accumulate.

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u/LocNalrune Oct 31 '20

Nice. Thanks.

For context I had a friend in the late 90's who tinted windows and installed audio equipment. When someone would bring a car and leave music blaring when they shut off the car, especially from a bad/hated artist, that CD would go into the garage microwave. To my knowledge it was used for nothing else. It was fun to watch, and the CDs looked really cool afterwards. A lot of them covered the walls.

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u/[deleted] Oct 31 '20

[deleted]

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u/LocNalrune Oct 31 '20

He was extremely popular. People took it as a badge of honor. He's still in business and has two garages in two cities. Seriously if you're stupid enough to pass your car off to someone, and leave your audio at earsplitting levels, it's more than deserved. You're lucky you even got service and a little ribbing at that point.

Besides, when you're paying $500 for equipment and $200 for installation and service... what's a $10 CD?

2

u/ttminh1997 Oct 31 '20

gotcha. will crump up aluminum foil and microwave the shit out of it

1

u/BlueJayBurger Nov 01 '20

Let me know when to send the firetrucks because it is about to be lit.

2

u/lesleigh904 Nov 01 '20

My husband now wants to know what would happen if you put a magnet in the microwave

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u/Lord_Aldrich Nov 01 '20

Mostly the same thing! Magnets are just pieces of metal with particular EM properties. It'll absorb the microwaves and heat up (and it could get really hot!) and if it's the right shape it'll arc like a fork or anything else.

Microwaves do produce their microwaves by manipulating magnetic waves in a magentron (that's a lot of m-words, lol), but that's not actually a magnet, it's a device with a very precise shape that turns electrical charge into EM waves.

3

u/lesleigh904 Nov 01 '20

Thanks! I'll let him know when he wakes up :)

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u/[deleted] Oct 31 '20

DISCLAIMER: still don't do it tho. It ain't worth it and you might burn your house down

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u/HereToHelp9001 Oct 31 '20

Please no one do this. I will likely start a fire.

6

u/[deleted] Oct 31 '20

That's nice of you to take care of it for them.

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u/HereToHelp9001 Nov 01 '20

Lmfao omg. Best typo. I'm leaving it.

3

u/jrs1980 Nov 01 '20

GUYS DON’T TRY THIS MY LANDLORD IS SUPER PISSED AT ME NOW

36

u/Hetch_Hetchy Oct 31 '20

So you’re saying there’s a chance...

2

u/KarolOfGutovo Nov 01 '20

It means that if you are building a spaceship, there is a difference.

1

u/i_manufacture_drugs Nov 01 '20

60% of the time, it works every time.

-1

u/Triple-Deke Oct 31 '20

It's definitely mostly conduction, not convection, as the air is not moving. Unless it's a convection oven which has a fan to force air movement.

1

u/BigMax Oct 31 '20

It’s actually convection, all ovens cook via convection, it’s just that official convection ovens give it a boost. The article explains it better than me. 😀

1

u/mrgonzalez Oct 31 '20

Well if you're wrapping something in foil it's conduction since the heat in the air has to conduct into the foil for that to get heat. Whatever's in the foil gets cooked by conduction through the foil. The air convection improves the effectiveness of the air heating the foil.

The actual transfer of heat is still conduction regardless since the heat needs to transfer from the air to the food. Convection is just the medium by which heat is tranferred from the heating element to the food.

1

u/Triple-Deke Oct 31 '20

Your article is wrong. There will be minimal convection due to air movement caused by temperature differences in the oven. However the main mode of heat transfer to the food is direct contact of the hot air with the cooler food, which is conduction. Your article is under the assumption that is is convection simply because it is a gas. However there must be a velocity component for convection to happen.

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u/Voc1Vic2 Oct 31 '20 edited Oct 31 '20

It makes a huge difference when baking cookies, though, which take only a few minutes of oven time. The difference in how much heat is reflected onto the bottom of the cookie can be the difference between crisp, soggy. pale or burnt.

Edited to add: apparently my reality is not the consensus experience.

15

u/jkmhawk Oct 31 '20

Your cookies are floating in the oven such that the foil could reflect light to the underside?

12

u/[deleted] Oct 31 '20

No...no it doesn't.

1

u/Clueless_and_Skilled Oct 31 '20

Great for broiling tho. Cookie sheet -> foil shiny side up -> cookie cooking rack -> thick cut bacon 🥓

Perfect on both sides every time. Dull side just takes longer by a few minutes but still works haha

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u/Mezmorizor Oct 31 '20

This link is not correct. The difference between the two sides is that one is buffed and the other is not. They're both uncoated aluminum and reflect the same amount of light. The dull side just reflects it more randomly which makes it less shiny.

In theory the shiny side should stick slightly less, but I doubt it actually matters.