T

Why does tin foil not burn you when you touch it? When I was a kid, it did.

6 Answers
Did they change the design somehow?
H

One, your fingers aren't nearly as delicate as they were when you were a kid. Two, a standard roll of tin foil today is much thinner than what it once was. Even the heavy duty is not a thick as the heavy duty of yesteryear. Being thinner (lighter) the heat dissipates more quickly.

The combination of more mature fingers and thinner foil is why you are less likely to get burned by tin foil today than when you were a kid.

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P

It is probably as Hellku27 suggests likely to be due to more mature fingers. As we get older, we develop callouses and layers of dead skin cells on areas of skin which are subjected to regular friction or pressure. So for example you get callouses on your palms at the base of your fingers if you do a lot of manual work such as gardening or using hand tools. If you walk a lot, or spend a lot of time on your feet, you can get them on the underside of your toes. I even have a small one on the underside of my wrist at the base of my hand where it rubs the surface of my laptop (from spending hours typing and surfing!)
Callouses are rough and more thermally insulating than regular skin. So if you touch something hot momentarily, heat doesn't transfer as quickly through this skin. One of my "party tricks" is to clean the molten solder from my soldering iron by wiping the tip with with my bare fingers. This can be done without getting burned if you are quick enough! This is similar to how people don't get burned when walking on hot coals. If your hands are sweaty, this would also make it less likely to get burned as water absorbs a huge amount of water when heating up or boiling. It is also a bad conductor of heat and would act as an insulating barrier between the foil and your fingers.
As regards the foil being thinner, This shouldn't radiate the heat away quicker since the surface area is the same. However being thinner, the thermal mass is less and so the foil contains less heat to be absorbed by the fingers (a tiny drop of boiling hot water falling on your skin won't burn you badly because the thermal mass is small).

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B

Whether or not you burn yourself when you touch a material depend on the total amount of heat stored in that said material which in turn will determine by how much the temperature of your skin will be increased by. A thin metal foil contains very little mass, and as the heat capacity is directly related to the mass of the material, even if the temperature is high of the metal foil, the heat energy within is actually very limited. Thus, when you touch such a thin foil, your body, or finger, will rapidly absorb the heat, while cooling down the foil. However, due to the limited amount of heat energy within the foil, the temperature of your skin will not be elevated by many degrees at all, therefore you do not burn yourself.

On the other hand, if you touch the pan that has been in the oven, you will burn yourself. This is because the pan is of higher mass, thus containing more heat energy. When you touch it, the heat energy will continuously flow to your skin and cause a significant increase of the skin temperature, causing a burn on your skin.

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S

I don't know what kind of foil you use that will not burn human skin. Hot aluminum foil will burn your fingers if you touch it. In fact I got burned just last week.

I wrapped the edge of a pie in aluminum foil to prevent the crust from getting too brown. When I opened the oven to check the pie the foil had fallen off. I burned my fingers when I tried to put it back.

I did not burn myself on the pie either. I burned myself on the foil.

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S

I am sure they still would burn you if it is hot enough. Aluminium foil is nmore commonly used nowadays. There are some aluminium foils which are thicker. Heat dissipates quite quickly from the foil. What is keeping it hot, is the heated material contained within. If the foil is thick, you may not get burned that easily.

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S

Good reasoning, Elaine.

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