How to heat insulators work?

Question

Polystyrene (styrofoam) is a good insulator, but air is an even worse insulator. Why then, do people keep items in polystyrene boxes instead of leaving them exposed to air? How exactly do these insulators like styrofoam work? I would appreciate if you make references to the molecules of the materials.

Answer 1

As above but remember there are 3 ways of transmitting heat.

Conduction (along a liquid, gas or solid) for example wood is a poor conductor of heat is a good one this is because metal has free electrons and these move to conduct heat away from more energetic areas to less energetic ones in a manner very similar to the way electricity moves through a conductor (that's how it got its name)

Convection this is gas and liquid only where movement of the molecules of the substance cause a sort of osmosis moving away from the hotter places to cooler once taking the heat they pick up along the way.

Radiation (works even in a vacuum) where the body itself emits infrared radiation  and if its surroundings are cooler then there is a nett loss of heat to the surroundings.

Styrofoam works on 3 levels the polystyrene is a poor conductor off heat so reducing the conduction losses., it contains trapped bubbles of air (better insulator than pS) but because they are trapped it cannot lose heat by convection.

the Styrofoam quickly heats up to the same temperature as the contents and reduced heat loss by radiation internally and because its such a good insulator the outside stays cool so reducing heal loss by radiation from the outside and ends up setting up a temperature gradient from the insides to the outsides.

Answer 2

As you said, expanded polystyrene is a better heat insulator than air.

Still air is a very good insulator, but in open air you get convection currents that transfer heat from one place to another. The reason expanded polystyrene is so good as an insulator is that it contains bubbles of trapped air, so it stops convection currents.

The other reason you would want to keep things in a polystyrene box is that when you put an object on a surface it can transfer heat to or from the surface by direct conduction. The polystyrene isolates it from the surface.

Edit:

Oh yes, molecules... Gases are better insulator than solids and liquids because they have fewer molecules per unit volume. Since it is energy transfer by molecules that is responsible for heat conduction less heat is conducted by gases.

Liquids are the worst insulators because they have a high density of molecules and they have convection currents.