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Former process engineer in an aluminum factory. Aluminum foil is only shiny on one side and duller on the other for process reasons, not for any "turn this part towards baking, etc" reasons.
It's just easier to double it on itself and machine it to double thickness than it is to hit single thickness precision, especially given how much more tensile strength it gives it.
Also, our QA lab did all kinds of tests on it to settle arguments. The amount of heat reflected/absorbed between the two sides is trivially small. But if you like one side better you should wrap it that way, for sure!
The amount of heat reflected/absorbed between the two sides is trivially small.
Your particular choice of wording here makes me very curious: Do you mean that there really was a measurable difference (which was trivially small)?
Yup, the lab could tell a difference! Shiney side (so mill roller facing, as opposed to the dull side which faces the other layer of aluminum) was marginally more reflective, but I believe (and a former coworker also remembered it as) it was less than a tenth of a percent (<0.1% for the visual folks)
Anyone who says it affects cooking time or something is mistaken, I'd wager.
Yup, the lab could tell a difference!
Awesome!
Jokes on you.
I baked my casserole with the shiny side up and pulled it out at 59 minutes and 55 seconds, when it was supposed to go for an hour.
So take that Dull Side!
Welcome to the Dull Side.
Such men are dangerous!
Today I learned numbers are visuals but words are not. Wtf dude!
Now that's the kind of industry secrets I opened this thread for.
Any info on surface roughness? I'm thinking shiny side would be smoother and therefore less sticky, though I don't know how much the passivation layer would affect it. Probably no where close to making a difference at the end of the day, but I'm curious.
It was a fair few years ago, but yeah, the oxidation on it will be so much smoother than the delta in surface roughness that I doubt it'd make much difference. Lemme reach out to a metallurgist from there and see what he thinks!
Post your spectral emissivity study or GTFO!
I mean, maybe if you bake a stone cold potato that was in the fridge and then cook it for two hours? But even then we're probably talking about a handful of minutes at the most.
Okay, my buddy is gonna take foil tomorrow and run it over the profilometer (?) tomorrow and see. I'll report back with more numbers and less hand waving when I have it
I'll be here to read those numbers
I'm an engineer in a totally different industry but I want to know what the numbers are
If the Internet has taught me anything, they’re 42 and 69.
Matte side isn't non stick?
Correct. Just a manufacturing decision. It looks a lot more different than it actually is.
Update: sorry to be an OP who didn't deliver. My buddy never made the measurement. I'm hoping he will. Sorry everyone!
Reynolds wrap literally has this as a faq on their website because so many people think it.
This is all I found on their site about it, which aligns but isn't as much detail as I hoped
With standard and heavy duty foil, it’s perfectly fine to place your food on either side so you can decide if you prefer to have the shiny or dull side facing out.