Why is polystyrene a good sound insulator?

Answer 1

The characteristics that make polystyrene is a good insulator stem from its composition of long polymer chains and because it encapsulates regions of gas in the form of a closed cell foam. (The form used in insulation is often a closed cell foam, but that is not the only form taken by polystyrene.)

Thermal conductivity of metals is high because the electrons are effective in transferring heat. Polystyrene is not a metal and so, like most other nonmetallic materials, its basic thermal properties are understood in terms of the vibrations and motions of its constituent atoms and molecules. Propagation of heat is the transfer of energy of atomic and molecule motion from one region of a material to another. (Hot to cold, or regions with a lot of vibration and motion to regions with less.) The effectiveness of such propagation depends on the details of molecular interactions and whether they vibrations in on molecule are strongly coupled and easily transferred to nearby molecules. So, a real answer to the "why" part of the question is rooted in detailed analysis at the atomic level. A more abbreviated response asserts that polymers in general do not have features that enhance heat transfer. Polymers are strong because they have long molecules and these may be chemically bonded and cross linked, the coupling of vibrations from one part of a molecule to another or one molecule to the next are not as strong as something like a traditional crystalline solid where every atom is rigidly connected to all of its neighbors. So, the general amorphous character of polymers is automatically a hindrance to thermal conductivity.

That said, the additional insulating properties of a foam are actually more important. Gases have poor thermal conductivities as long as heat transfer by convection can be minimized. Small volumes have a small degree of convection, so closed cell foams automatically benefit from the good insulating properties of the enclosed gas and the poor convection properties created by enclosing the gas in small volumes.

In summary, plastic polymers in general and polystyrene in particular, have poor thermal conductivity and hence good insulation because of the details of the molecular structure and interactions. In addition, the form of polystyrene used for insulation has small enclosed cells of gas that are themselves poor conductors of heat.

Answer 2

Polystyrene foam is a good insulator.

The characteristics that make polystyrene is a good insulator stem from its composition of long polymer chains and because it encapsulates regions of gas in the form of a closed cell foam. Air and gas in general are poor conductors of hear when convection is inhibited as it is in a foam. (The form used in insulation is often a closed cell foam, but that is not the only form taken by polystyrene.)

Answer 3

Polystyrene is neither sufficiently porous nor of sufficient mass to be either a good Sound Absorber, or a Sound Barrier. [Those are the proper technical terms.]

Answer 4

Polysterene does not have free electrons which are required for conduction of electricity.

Answer 5

It contains a lot of air spaces.