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Does the material the container is made of affect its ability to retain heat?
Question Date: 2014-08-07
Answer 1:

Absolutely! All materials fall somewhere in the spectrum of heat conductors and insulators. For a container that is intended for insulation, you want a material that has a low thermal conductivity (i.e. it can sustain large temperature gradients). To understand how to retain heat, you'll need to know how heat travels. You can see the table below
see table for a range of thermal conductivities in various materials. This table was taken from the link
click here to read it.

The units of thermal conductivity are Watts (or Joules per second) per meter Celsius. It's a measure of how much heat (i.e. energy) is transferred per unit time across each unit of area per unit temperature. Note that these are only for 25 C. Thermal conductivity is temperature dependent! In fact, at high enough temperatures, you can insulating materials conducting.

How does heat travel?
From everyday intuition (and many years of thermodynamics), we know that heat tends to travel from hot to cold. There are several mechanisms that heat is transferred between two bodies of different temperatures. The modes of heat transfer are:

- advection: transport by fluid via fluid motion
- conduction: transfer by physical contact
- convection: transfer by contact between physical object and environment via fluid motion
- radiation: generated by thermal motion of charged particles into light

The one you may be most familiar with is conduction (e.g. when Convection could technically be seen as a form of conduction if you view the gas as a collection of particles that transfer energy via collisions with itself and the physical object.

What makes an insulator an insulator?
It turns out that materials that are good electrical insulators also tend to be good thermal insulators. Metals are good conductors mainly due to the fact they have essentially free electrons, which carry heat with them when conducting. The reason for this can be roughly traced back to what you learn in chemistry- metals tend to want to give up electrons to achieve a stable octet, so they tend to hang on to valence electrons less strongly. It's pretty surprising how much intuition you can have about a material simply from its position on the periodic table. In contrast, insulators have very localized electrons that do not conduct well; heat travels through insulators via lattice vibrations, also known as phonons.

A cool application is a vacuum-insulated thermo. Most thermos containers are just insulated with a layer of air, so why a vacuum? A vacuum has nothing in it- no particles, not even dust- so heat exchange can't happen through conduction or convection! But of course, this would have to be a perfect vacuum, which is pretty hard (and expensive) to achieve. What would happen if thermos were instead insulated with wood? Would you still expect your hot drink to be as hot a few hours later? For reference, the thermal conductivity of a vacuum is nearly zero.

Another interesting thing to muse about: Why is it that tile, such as in your bathroom or kitchen, feels cooler than the carpet, even though they are at the same temperature? Think about it, and then watch this video
about the nuances between heat and temperature to find out more.

Hope this helps!

Answer 2:

Yes - different materials are different conductors of heat. Metal in particular is especially bad, while ceramic is much better. This is why coffee cups and mugs are made out of china (a ceramic), and not out of metal or glass. Air is an even worse conductor of heat, so a thermos with a layer of air between its inner and outer layers is even better yet at retaining heat.

Answer 3:

Styrofoam is a great container because it retains the heat of its contents so well. The reason styrofoam works so well is that it is mostly air. This is also why it is so crunchy and light. A styrofoam container helps retain heat because it insulates the contents from the environment. Mostly, this is because the large pockets of air in styrofoam prevent heat from passing through it, and this prevents heat flow.

This is very different than a metal, which conducts heat really well, and so a beverage or other contents inside a metal container will change temperature much more quickly.

Answer 4:

There is a property that pertains to all materials called its heat capacity. This quantity is the ratio of the amount of heat that is added or removed from an object to the change in temperature resulting from the heat change. Make sure to note that heat and temperature are actually different things. Temperature refers to an average energy of the particles that make up a system, whereas heat is the transfer of this energy from the particles to its surroundings (or from the surroundings to the particles).

So to get to your question, different types of materials have different heat capacities. Some change temperature quite a bit when heat is added or removed while others require a lot more energy to change temperature. For example, think about boiling water on the stove. Most metals have a relatively low heat capacity, so if you placed just a metal pot on the stove and turn the stove on, the pot would become burning hot very quickly (it didn't take much heat transfer to change the temperature of the metal). But now, if you add water in the the pot before boiling and then turn on the stove, it takes longer for the metal to heat up because the energy is also being transferred to the water, which has a very high heat capacity, and requires much more energy input to change temperature.

So yes, all materials have their own characteristic heat capacity, which effects how well the material can retain heat and varies for different materials.

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