Styrofoam is a plastic product and it is known to contain a lot of air bubbles in it. Due to the presence of air bubbles, it is considered as intense conductor of heat. Normally a thermal insulator is a substance that will reduce the transfer of heat. An insulator generally reflects heat and does not emit heat from inside. It was found that the density of the material is inversely proportional to the ability of its heat conduction. It means that materials with less density can cease heat conduction very well compared to those with more density. Gasses act as insulators of heat as they are very less dense.
Styrofoam is made of polystyrene. It is called as foam as it has gas bubbles present inside. Polystyrene is a common plastic form and since it resides air bubbles, it gets transformed into Styrofoam. The foam cells with air are closed and provide an opportunity for the material to exhibit insulating property. Moreover, transfer of heat takes place when the atoms are moving continuously. The movement of atoms pushes the heat favorably in a hot material. If the atoms are spread into various different areas, then the heat cannot get transmitted properly in that material.
If heat reaches an insulator, it cannot travel into it. Styrofoam will also prevent the heat transfer through it effectively. This makes it be called as an excellent insulator. Styrofoam has very little plastic in it with most of its material being filled with air bubbles. The part of plastic that can conduct heat is very less and hence it works as an insulator.
When a hot material is placed in the open air, the air adjacent to the material will get heated and it rises up. Immediately, cool air reaches near the material. It gets heated and again moves up. Like this, a chain of heat currents will be created. This is called convection current. The gas bubbles are so small in the Styrofoam that they cannot form convection currents to make the material to be a good conductor of heat. Hence, Styrofoam is a heat insulator.