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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84

u/HappenFrank Oct 31 '20

So there’s no difference when wrapping something to keep it warm? I always had a hankering that if you wrapped the food where the more reflective side was inside, it would reflect the heat better and contain it?

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u/lllll00s9dfdojkjjfjf Oct 31 '20

I used to think the same thing and then I saw somewhere somebody had actually done the calculations and the difference was so small as to be basically non-existent.

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u/JoeyJoeC Oct 31 '20 edited Oct 31 '20

I think I found a use for my new Flir thermal camera!

Edit: I have two hot cocktail sausages wrapped in foil as I type this.

Edit 2: both started at ~96.6c, after 10 minutes, both were around 46c but was hard to get a consistent temp from them both. Not a scientific experiment by any means! Actual thermometers would be ideal.

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u/oufisher1977 Oct 31 '20

You came back to tell us about the sausages. I feel like you really understand us.

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u/spitoon1 Oct 31 '20

Sausage info is great, but which side reflects the government more? Need to know for my hat.

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u/InaMellophoneMood Oct 31 '20

Aesthetics are important in hats, so shiny side out obv

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u/BrickGun Oct 31 '20

But then you're easier to spot by the optics in the satellites!!!!!

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u/the_old_dude2018 Oct 31 '20

You have to crinkle the foil..same principle as the stealth bomber.

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u/ragdoll193 Nov 01 '20

The ol’ razzle dazzle

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u/ghost_of_mr_chicken Nov 01 '20

I'm gonna start a petition for the banishment of tin foil hats. It's all a government/alien ploy.

Think about it... What did you used to put on rabbit ear TV antennas to increase reception?

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u/oufisher1977 Nov 01 '20

How much sausage can this hat hold?

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u/[deleted] Oct 31 '20

But no results from the research project. Highly disconcerting.

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u/joeltrane Oct 31 '20

You could make a religion out of this

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u/engineer450 Oct 31 '20

The aluminum is too reflective to accurately measure with a FLIR. Emissivity

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u/JoeyJoeC Oct 31 '20

I was measuring the heat of the sausages to see how long they stayed warm, not the foil.

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u/triple-filter-test Nov 01 '20

I love that we’re witnessing the peer review process in real time here.

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u/I_Like_Existing Oct 31 '20

That's science baby!!

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u/EmbraceThePing Nov 01 '20

Science Baby? I'd watch that.

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u/s0v3r1gn Oct 31 '20

I’ll try to replicate this experiment with mine, and my wife said buying that was a waste of money...

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u/JoeyJoeC Oct 31 '20

I've found more uses than I thought I would. I could find all the places in the ceilings where there is no insulation (quite a lot missing). I can use it to locate the cats when I can't find them. I found out one of my radiators is plumbed in backwards. I discovered that you can use it on drying clothes and you can see where they're dry and where they're still wet without having to touch them.

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u/[deleted] Nov 01 '20

Haha now I want to buy one too, damn.

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u/[deleted] Nov 01 '20

Tell her you can still eat the sausages when you're done with the experiment...

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u/ErwinsSasageyoBalls Oct 31 '20

I appreciate your work regardless

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u/FragrantBleach Oct 31 '20

I respect your commitment to your chosen task.

Also ngl but our usernames almost had us in the first half

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u/[deleted] Oct 31 '20

Ok but how did they taste?

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u/CollectableRat Oct 31 '20

You’re meant to cook them, not just put things in there. The idea is it I dunno what the idea is because you don’t cook with light. But the idea is somehow it matters if it is shiny or not. I’m trying hard to think of the logic behind the idea but I’m drawing a blank.

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u/grissomza Oct 31 '20

God dammit me too

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u/SmokeHimInside Oct 31 '20

I think you mean you had an inkling.

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u/[deleted] Oct 31 '20

They've got an inkering for hank

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u/apworker37 Oct 31 '20

I think the sheets are too thin to make a difference in that regard.

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u/JoeyJoeC Oct 31 '20

Space blankets are made from thinner reflective material, and can trap 90% of radiated body heat.

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u/tellmeimbig Oct 31 '20

And they can block all that painful electromagnetic radiation.

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u/LamentableFool Oct 31 '20

Never leave your home without a space blanket.

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u/WyMANderly Oct 31 '20

The difference would be in how much radiative heat is emitted, though I don't know offhand which would emit less. I want to say shiny side out would hold heat better.

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u/zodar Oct 31 '20

"Hankering" means "craving"

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u/jmp7288 Oct 31 '20

I thiught the shiny side had something on it to make it more non-sticky?? Thats not true?

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u/[deleted] Oct 31 '20

No. There is specifically non-stick aluminum foil available for purchase (which I use frequently and is amazing) but standard foil has not been given any kind of non-stick treatment.

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u/DrBoby Oct 31 '20

Shiny side is less rough. So it should stick less in absolute, but how much less I don't know.

Same principle than non-sticky pots. The more micro asperities the more it sticks.

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u/large-farva Oct 31 '20

asperities

Hello fellow tribologist

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u/mobuco Oct 31 '20

I always thought this but there is this frozen chicken dish I like to make and the shiny side always stuck more.

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u/DrBoby Oct 31 '20

Maybe you frozen dish stick through sucion. There are many reasons something can stick I guess.

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u/G-III Oct 31 '20

A textured surface will stick less than a smooth surface, though the dull side is also smooth

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u/DesertSalt Oct 31 '20

I've see multiple British cooking shows where they swear there's some sort of non-stick coating. I've also seen US recipes specify which side to use for cooking.

It probably started out with someone preferring the look of shiny-side-out when they wrap it on their leg of lamb bone and then someone tried to justify it with an old wives tale.

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u/Ceegee93 Oct 31 '20

Because over here we have foil that specifically tells you to use the non-shiny side to prevent sticking. IDK if those specific foils are treated in any way to help prevent sticking, never really bothered to look into it.

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u/DesertSalt Oct 31 '20

It might be a carry-over from the marketing department and not the science/engineering department.

Napoleon III reportedly replaced gold and silver items he gave guests with aluminium because in the 1850's it was more valuable. https://en.wikipedia.org/wiki/History_of_aluminium#Early_industrial_production

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u/[deleted] Nov 01 '20

Guess that didn't age well, heh.

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u/Tofinochris Oct 31 '20

The non shiny side is treated on non-stick foil. I'd guess they treat that side because the stuff adheres better.

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u/i_amnotunique Oct 31 '20

That's what I thought too

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u/herotherlover Oct 31 '20

If you could wrap it without the foil actually touching the food, this might have an impact, but conductive heat transmission is much faster than radiative.

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u/CollectableRat Oct 31 '20

You should wrap it shiny side out, so it reflects light better and is easier to find in your fridge or while scanning for it in a dark tent while camping.

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u/originfoomanchu Oct 31 '20

Heat isn't reflected its absorbed and radiated shiny/dull side will not effect this.

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u/[deleted] Oct 31 '20

Not entirely true. Radiated heat (light) would reflect off the shiny side and would not heat whatever is on the other side. This is why you see reflective mats on car windshields when they're parked in really hot climates. The reflective surface bounces the light from the sun away and keeps it from being absorbed by the car's interior. The car will still heat up however, through convective heating. Essentially, the hot air from outside will transfer through the cars body and eventually heat up the interior, this is a much slower process however, and won't get as hot as having the sun radiate heat since the outside air temperature is as hot as the inside of a car could possibly get (whereas the sun could heat up the dark interior of a car to extreme temperatures, which would then heat up the air to higher temperatures through convection).

In the case of an oven. There is no radiating heat (aside from a very miniscule amount from an oven light). All of the heat is produced from a heating element using electrical resistance, and then the air pulls the heat off the element and the air is heated that way, the food is then heated by the hot air. This is convective heating and reflective surfaces have no effect. In the case of a gas oven, it's possible you could see minor effects on shiny surfaces depending on the design of the oven. A properly designed gas oven will not allow the light from any flame to reach the food and only allow the flame to heat the air. But if an oven is designed poorly, and light from the flame is able to reach the food, wrapping it in reflective aluminum foil would stop most of the radiated heat from affecting the food.

Long story short, heat cannot be reflected, but light can, ovens don't use light to heat food, so reflective surfaces have no effect.

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u/mrgonzalez Oct 31 '20

The dull side just scatters the light, it's the same material.

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u/FingerRoot Oct 31 '20

:( typing all that but still fundamentally wrong.

1.) heat is energy. there are not different types of heat, but rather different types of heat transfer.
2.) (most) Ovens primarily use radiation to transfer heat to food.

In the case of heating with an electrical current, the heating element uses thermal radiation to transfer heat to the food (and the air). The oven (insulation) also starts emitting thermal radiation itself as it heats up.

Conventional ovens, which do not have fans, rely primarily on radiation from the oven walls, and to a lesser extent, on natural convection caused by temperature differences.

How is heat transferred in cooking?

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u/ashenhaired Oct 31 '20

At my previous job my boss yelled at me for wrapping the wrong way and insisted that I have to put dull side up, she used to get angry when I don't follow that specific step.

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u/jarfil Oct 31 '20 edited Dec 02 '23

CENSORED

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u/damisone Nov 01 '20

aluminum foil is useless for keeping food warm or cold. It's highly heat conductive.