Why isn't rubber a better thermal insulator than styrofoam?

[OmegaKV]

I haven't studied materials in depth, but I would assume that something like rubber would make a good insulator because of its bounciness. The molecules of a substance contained in a rubber container would collide with the walls of the container in a very elastic collision, and the kinetic energy of the substance would be conserved.

 

[The Bill]

You might not be comparing materials of similar structure. You said nothing of the structure of the rubber, nor which chemical type of rubber you are comparing. Styrofoam(foamed polystyrene) has a low thermal conductivity because it is a foam. Foamed rubbers can also have low thermal conductivity. Foamed neoprene is used in wetsuits for this reason. Its thermal conductivity is almost as low as foamed polystyrene, but it is much more flexible. Foamed neoprene is also used in those bottle/can koozies which are used to keep cold drinks cold for a bit longer.

 

[davenn]

Styrofoam(foamed polystyrene) has a low thermal conductivity because it is a foam.

because its structure is predominantly air and air is a poor thermal conductor

 

[NascentOxygen]

I haven't studied materials in depth, but I would assume that something like rubber would make a good insulator because of its bounciness. The molecules of a substance contained in a rubber container would collide with the walls of the container in a very elastic collision, and the kinetic energy of the substance would be conserved.

Rubber is not a very elastic material, and an impact that briefly stretches it loses energy. A substance that is good for demonstrating low-loss elastic collisions is quartz glass. If you drop a marble onto a slab of rubber, then onto a slab of quartz, the rebound is higher from the quartz because quartz is a very elastic material.

The term "elastic" has a precise meaning in physics. (You can see how it differs from the street vernacular where the word "elastic" just means stretchy.)