Polystyrene (PS) is a synthetic aromatic hydrocarbon polymer made from the monomer styrene. Polystyrene can be solid or foamed. General-purpose polystyrene is clear, hard, and rather brittle. It is an inexpensive resin per unit weight. It is a rather poor barrier to oxygen and water vapor and has a relatively low melting point. Polystyrene is one of the most widely used plastics, the scale of its production being several million tons per year. Polystyrene can be naturally transparent, but can be colored with colorants. Uses include protective packaging (such as packing peanuts and CD and DVD cases), containers, lids, bottles, trays, tumblers, disposable cutlery  and in the making of models.
As a thermoplastic polymer, polystyrene is in a solid (glassy) state at room temperature but flows if heated above about 100 °C, its glass transition temperature. It becomes rigid again when cooled. This temperature behavior is exploited for extrusion (as in Styrofoam) and also for molding and vacuum forming, since it can be cast into molds with fine detail.
Polystyrene is slow to biodegrade. It is accumulating as a form of litter in the outdoor environment, particularly along shores and waterways, especially in its foam form, and in the Pacific Ocean.
Polystyrene was discovered in 1839 by Eduard Simon, an apothecary from Berlin. From storax, the resin of the American sweetgum tree Liquidambar styraciflua, he distilled an oily substance, a monomer that he named styrol. Several days later, Simon found that the styrol had thickened into a jelly he dubbed styrol oxide ("Styroloxyd") because he presumed an oxidation. By 1845 Jamaican-born chemist John Buddle Blyth and German chemist August Wilhelm von Hofmann showed that the same transformation of styrol took place in the absence of oxygen. They called the product "metastyrol"; analysis showed that it was chemically identical to Simon's Styroloxyd. In 1866 Marcelin Berthelot correctly identified the formation of metastyrol/Styroloxyd from styrol as a polymerization process. About 80 years later it was realized that heating of styrol starts a chain reaction that produces macromolecules, following the thesis of German organic chemist Hermann Staudinger (1881–1965). This eventually led to the substance receiving its present name, polystyrene.
The company I. G. Farben began manufacturing polystyrene in Ludwigshafen, about 1931, hoping it would be a suitable replacement for die-cast zinc in many applications. Success was achieved when they developed a reactor vessel that extruded polystyrene through a heated tube and cutter, producing polystyrene in pellet form.
Otis Ray McIntire (1918-1996) a chemical engineer of Dow Chemical rediscovered a process first patented by Swedish inventor Carl Munters. According to the Science History Institute, "Dow bought the rights to Munters’s method and began producing a lightweight, water-resistant, and buoyant material that seemed perfectly suited for building docks and watercraft and for insulating homes, offices, and chicken sheds. In 1944, Styrofoam was patented.
Before 1949, chemical engineer Fritz Stastny (1908–1985) developed pre-expanded PS beads by incorporating aliphatic hydrocarbons, such as pentane. These beads are the raw material for molding parts or extruding sheets. BASF and Stastny applied for a patent that was issued in 1949. The molding process was demonstrated at the Kunststoff Messe 1952 in Düsseldorf. Products were named Styropor.
The crystal structure of isotactic polystyrene was reported by Giulio Natta.
In 1954, the Koppers Company in Pittsburgh, Pennsylvania, developed expanded polystyrene (EPS) foam under the trade name Dylite. In 1960, Dart Container, the largest manufacturer of foam cups, shipped their first order.

Ordinary polystyrene

Used for general use, polystyrene called GPPS
Usually, it must have properties such as good heat resistance, good compression and fluidity during the process. These polystyrene have high dielectric properties and are therefore of great use in electrical applications. The brand of this product is on the Crystal Market in Iran.
For the production of disposable containers, electronic equipment, watch cases, TVs, radios, sports goods, toys, refrigeration systems, refrigerators, freezers and household appliances.

Resistant polystyrene
HIPS (high-impact polystyrene) This type of polystyrene is an abbreviation
Containers are shock resistant and therefore used in the construction and body of appliances. The brand of this material is on the market in Iran Hymkent.

For the production of sporting goods, toys, refrigeration, refrigerators, freezers and household appliances and disposable utensils.
Expansion Polystyrene (yonolite)
A kind of white polymer to which they have an Expanded polystyrene (EPS). This type of polystyrene is abbreviated Foaming agent has been added; it is known in Iran as Yonolite.
For the production of ceiling elastomer blocks for use as sound insulation and thermal insulation in buildings and places.
Refrigeration insulation in cold stores and industrial refrigerators.
Making all kinds of foam packaging and all types of refrigerators and thermos.

EPS block ceiling elasto block properties
Production of ceiling elastomeric blocks
The new ceiling block is made of expandable polystyrene materials and is the best replacement for cement and clay blocks.
EPS block ceiling elasto block properties
1- Lightness
2. Speed and ease of implementation of the ceiling
3. Sustainable against earthquake: Due to lower dead weight, it is more stable in the earthquake and is not crushed during an earthquake.
4. Saving on plaster and soil: For the first time, grooves on the lower side of the block are created and placed under the roof.
5. Saving on hardware: 22% per square meter.
6- Impact
7. Fast and easy shipping
8 - Reduction of 15 tons per 100 square meters
9. High speed on implementation and lower wage costs
10 - Saving in the concrete beams of the ceiling so that the distance between the axis of concrete beams can be changed from 50 centimeters to at least 60 centimeters