Metal baking pans vs. silicone

Paul, I'm a bit uncomfortable with your use of the terms "conduct" and "insulate" here, as all materials are thermally conductive, just to vastly varying degrees. Stuart's point is key here: silicone has a far lower heat capacity than metal, and consequently transfers far less heat to the batter.

Geekily yours,
Mark Lipton

I was using the terms "conductor" and "insulator" in the layman's sense. Of course, scientifically speaking, we're dealing with differences in specific heat (the energy input to a substance required to raise its temperature by one degree), and with impedance, in the electromagnetic sense (of course we're dealing with infrared frequencies here).

Metals have both a very low specific heat (it takes very little energy input to raise their temperature), and very little resistance/impedance to transferring electromagnetic energy. This makes them what in layman's terms are called "conductors". In contrast, most ceramics, and silicone, have a higher specific heat and resistance/impedance, which makes them what in layman's terms are called "insulators". Muffins brown more readily in metal forms than in silicone because metal transfers the heat more readily than silicone does.

-Paul W.

Since we're nitpicking, how about making a baking pan out of aerogel? Technically it conducts heat, but most people would say it's an insulator. I saw some in person once--weird stuff.

http://en.wikipedia.org/wiki/Aerogel

I was using the terms "conductor" and "insulator" in the layman's sense. Of course, scientifically speaking, we're dealing with differences in specific heat (the energy input to a substance required to raise its temperature by one degree), and with impedance, in the electromagnetic sense (of course we're dealing with infrared frequencies here).

Technically, the two factors that determine thermal conducivity of a given material are specific heat capacity (aka "specific heat") expressed as energy/(volume/weight/amount)/temperature and thermal diffusivity, expressed as area/time. Good thermal conductors usually have a fairly high specific heat capacity, but especially a high thermal diffusivity. For instance, most metals have a volumetric specific heat capacity that is close to that of water (i.e., high) but differ tremendously in thermal diffusivity: Cu, 11161E-8 m^2/s vs. stainless steel, 405E-8 m^2/s -- which is why copper cookware is superior to stainless steel. Asbestos actually has a higher heat capacity than those metals, but very low diffusivity. Glass, too, has a low diffusivity (43E-8) and most plastics even lower (8-13E-8), which they combine with lower heat capacities.

Metals have both a very low specific heat (it takes very little energy input to raise their temperature), and very little resistance/impedance to transferring electromagnetic energy. This makes them what in layman's terms are called "conductors". In contrast, most ceramics, and silicone, have a higher specific heat and resistance/impedance, which makes them what in layman's terms are called "insulators". Muffins brown more readily in metal forms than in silicone because metal transfers the heat more readily than silicone does.

Low impedance isn't too important (I think) because radiative transfer involves absorption of electomagnetic energy by the material in question, followed by conductive transfer to the batter. Ceramics and silicone don't have higher specific heats than metals, but have much lower thermal diffusivity coefficients. However, I do agree with your last sentence

Geekily yours,
Mark Lipton

Since we're nitpicking, how about making a baking pan out of aerogel? Technically it conducts heat, but most people would say it's an insulator. I saw some in person once--weird stuff.

http://en.wikipedia.org/wiki/Aerogel

Yeah, aerogels are pretty crazy stuff and are about a poor a thermal conductor as you're likely to encounter.

Mark Lipton

Thank you, Jenise, for sharing the results with us. I had been curious about silicone pans... but no more!

Metals have both a very low specific heat

No, other way around. Besides the usual sources of thermal capacity, metals also have electronic specific heat because of the partially filled energy bands. That's the secret behind those meat defrosters- they're just a hunk of metal and their operation depends on them being able to absorb heat without much increase in temperature.

Sorry for the pedantry, I'm a geeky physical chemist.