Re: Why is aluminum foil not hot when it comes out of the oven?

Good observation, Zack, but you have reach the wrong conclusion about the 
aluminum not initially being hot.  Anything sitting in a hot oven tends to 
reach the same temperature as the oven high. (see note at the bottom)  So, 
say your mother is warming up a loaf of bread (maybe with some butter 
between the slices of bread) at 150 to 200 F.  When the oven door opens, 
that aluminum foil is at the 150 to 200 degrees as the oven.  However, 
notice that the aluminum foil is very thin.  There is very little actual 
aluminum and it is spread over a relatively large area (standard aluminum 
foil is about 0.0007 inches thick; heavy duty foil is about twice as 
thick).  As a result cool air outside the oven cools the foil quickly.  If 
your mother grabs the foil with her fingers, she is relying on the cool 
room air to cool the foil surface quickly to keep from burning herself.  
Also her fingers themselves have a lot more mass than the aluminum foil 
that they are in contact with so usually only the top surface of the skin 
would be heated.  Your mom's fingers might be a little toughened from all 
of her work buttering that bread so she doesn't notice a slight bit of 
damage to the surface layer of cells.  Also, if her hands are damp, the 
water on the surface of her hands will also cool the foil.

There isn't anything magic about the thin aluminum.  If the bread were 
wrapped in paper, you could also handle it directly from the oven.  The 
paper would, in fact, be less likely to burn your mom's fingers than the 
aluminum, since it doesn't conduct heat nearly as well.  (Unless of course 
your oven temperature is set too high and the paper starts on fire - but 
that is another story!)

The aluminum foil surrounding the bread is exactly the same material with 
the same properties as the aluminum cookie sheet that your mom uses to bake 
those chocolate chip cookies you love.  But the cookie sheet has much, much 
more aluminum (maybe 20 times as much aluminum) to retain the oven heat.  
Plus the cookies are cooking at around 400 F, so the starting temperature 
when removing the aluminum from the oven is much higher.  Your mother knows 
that she has to use a hot pad holder with a heated cookie sheet or she will 
get a bad burn.

Great observation, Zack.  And save a slice of bread or two for me.  
Buttered french bread is my favorite.

(Note: some people learning about radiation heat transfer might get 
confused by the fact that the aluminum foil is a highly reflective surface, 
thinking it might remain at a lower temperature.  Since the aluminum is 
essentially surrounded by a black body radiator as it is enclosed by the 
oven walls, it will reach the temperature of the oven, although at a 
slightly slower rate than if the foil adsorbed more radiation.  Maybe black 
aluminum foil for more rapid heating as a new product idea?)