EPS is consisted of closed cells which are glued together. It is rigid and tough and has good thermal insulation and damping property.
It is often used as packagings because of it can prevent damage and its thermal insulation required for food and medical transportation. It’s also used in building insulation.
The thermal conductivity of EPS varies from 0.032 to 0.038 W/(m·K) depending on its density. Recently the thermal conductivity has reached 0.029 to 0.034 W/(m·K) by adding graphite, aluminum and carbons as fillers and such EPS has grey or black color different from the normal white color.
It is normally produced by two meganism: 1. Polystyrene beads are expanded to little balls(pre-expanded polystyrene) with blowing agent like pentane. 2. The little balls are glued together with hot steam. In my thesis, we choose to use ready made pre-expanded polysyrene, because it’s easy to pour the little balls into the little cells of the panel.
There is another polystyrene foam called XPS(Extruded polystyrene). It offers higher surface roughness and stiffness. It has a reduced thermal conductivity between 0.029 and 0.039 W/(m·K). It has a higher water vapour diffusion resistance, which makes it more suitable in wet environment than EPS. One disadvantage of XPS is the use of hydrofluorocarbons(HFC) as blowing agent which has very high global warming potential.
There are two famous trade names of EPS. Styrofoam is a brand of XPS but is refered to EPS packaging in United States and Canada. Thermacol is another tradename originated from BASF.
There are a few disadvantages. It is non-biodegradable, but it’s recyclable although the recylcling program can be limited. It is flammable like other organic compounds. There will be rough panel edges and dust when cut, when XPS is cut clean and straight. It’s not water proof as XPS. It has a very low flexual strength while XPS has exellent flexual breaking strength.
Here is the reference link: http://www.wisegeek.com/what-is-a-polystyrene-foam.htm