What is Expanded Polystyrene Foam (EPS)? | The Definitive Guide

Hey mates. Today’s guide is all about the infamous foam material called EPS or expanded polystyrene. It is a material that has revolutionized packaging for both manufactured and consumers. So without further ado, let’s get started.

What is Expanded Polystyrene?

Expanded polystyrene, also known as EPS, is white-colored foam structured plastic material extracted from solid beads of polystyrene. The foam material has been around for many years now and has applications in many day-to-day used products. EPS has a closed-cell insulation structure. Its rigidness and lightweight make it quite handy for heavy load applications. The closed-cell structure is also responsible for low water and vapor penetration.

The foam material is produced mainly by two materials named Styrene and Pentene. Styrene is mainly responsible for cellular structure, and Penetne is used as a blowing agent.

Interestingly, a lot of times, EPS is also coined as Styrofoam™; however, that’s not the right term for expanded polystyrene.

Styrofoam™ is trademarked for closed-cell extruded polystyrene foam made for thermal insulation.

EPS Manufacturing Process – 

EPS manufacturing process

Manufacturing EPS is simpler than you might think. It’s a three-stage process. 1) Pre-Expansion, 2) Stabilization and 3) Molding.

Polystyrene is extracted from the petroleum product styrene, which itself is extracted from crude oil products. To manufacture expanded polystyrene, raw polystyrene beads are blended with pentene (which, as we discussed earlier, is a blowing agent).

Polystyrene granules must be performed at a temperature above 90°C. The high temperature will significantly evaporate the foaming agent and expand the thermoplastic materials 20 to 40 times to their original size.

Once the beads reach the desired size, they will be stored correctly for 8 to 12 hours to acquire a balanced state. Now it’s time for beads to make a visit to the shop floor and be used for the desired applications.

Interesting Read – What is PEEK Material? | Properties of PEEK | Limitations of PEEK | How PEEK is Manufactured? | Applications of PEEK

EPS Properties – 

EPS Properties

  • Mechanical Strength 
  • Thermal Insulation
  • Dimensional Stability
  • Water Absorption
  • Electrical Properties 
  • Chemical Resistance 
  • Fire Resistance 

1. Mechanical Strength:

EPS has great mechanical strength, making it suitable for numerous applications with high loads involved.

Depending on the application, EPS with high and low compressive strength can be utilized accordingly.

Normally, strength and related characteristics are affected by density. Still, EPS foam is mostly affected by the manufactured part’s geometry, and density plays a minor role in the size increase in EPS.

2. Thermal Insulation:

EPS consists of 98% air and has a closed-cell structure, making its thermal conductivity very low. The trapped inside the foam structure is a terrible heat conductor helping the foam with fantastic thermal insulation properties.

The following is the thermal conductivity of expanded polystyrene foam.

20 kg/m3 0.035
0.037 W/ (m·K) at 10 °C

3. Dimensional Stability:

dimensional stability

EPS in its polystyrene insulation is mostly known for its excellent dimensional stability, remaining virtually unaffected by surroundings. The maximum dimensional change recorded in EPS is a staggering less than 2%.

4. Water Absorption:

EPS does not retain moisture. When contacted with water, it absorbs a minimal amount of water. The water penetration is minimal through the foam through the tiny channels present in the fused beads.

5. Electrical Properties:

The dielectric constant for EPS foam is measured at a frequency range of 100-400 MHZ. The gross densities range between 20-40 kg/m3 lie between 1.02 and 1.04.

As EPS is extensively utilized in electronics and military packaging verticals, a molded version is optimized with antistatic agents.

6. Chemical Resistance:

Expanded Polystyrene is resistant to water, moist solutions, salt, and alkalis. However, for organic solvents, some caution is advisable.

7. Fire Resistance:

EPS of explosive, but modifications made in the retardants can greatly alter the foam’s combustion and minimize the flame spread.

Fascinating Read – What is LDPE Material? | The Complete Guide

Advantages of EPS – 

  • Excellent thermal insulation properties because it is mostly made of air.
  • Fabulous degradation resistance because of minimal water absorption.
  • EPS can be molded into many forms and thus can be utilized in a maximum number of applications.
  • It’s extremely lightweight, saving a lot of money on transportation.
  • Polystyrene foam has by far the best price/performance ratio compared to all the commercially available insulation materials.
  • It has sound absorption properties, which makes it quite useful in the construction industry.

Disadvantages of EPS – 

  • Largely Suspectibel to UV radiation.
  • Highly Flammable.
  • Poor chemical resistance to organic chemicals.

Styrofoam™ – 


Styrofoam is a Dow chemical company trademarked brand of closed-cell extruded polystyrene foam (XPS). It is also known as “Blue Board,” manufactured as a foam continuous building insulation board extensively used in walls, foundations for thermal insulation, and water barriers.

The material is usually light blue in color. It is most popular in applications in the United States and Canada. It comprises 95% air, making it unsinkable and capable of marinating its form for a prolonged time.

Styrofoam is mostly utilized for manufacturing containers, packaging materials, and coffee cups. The branded polystyrene foam is categorized by its roughness and the type of “crunch” it makes while being cut. It has moderate soluble properties, mixing with many organic solvents, cyanoacrylate, and propellents.

Applications of Expanded Polystyrene –

Applications for EPS

The main applications for Polystyrene foam can b found in industries like food packaging, Construction, Industrial packaging, and consumer goods.

1. Food packaging:

EPS is often used to produce continuous sheets utilized to manufacture food trays, dishes, and related packaging material that comes in handy for food storage and preservation.

It is mostly preferred for preserving dry foods like fruits, vegetables, meat, and seafood. EPS packaging is also vital for preserving the nutritional value of the cramped food inside.

EPS is not affected by fungal or bacterial attacks and is supremely safe for storing food. The thermal insulation properties play an important role in keeping fresh fr periods.

2. Industrial Packaging:

EPS foam has good shock absorption properties, making it an ideal choice for packaging and transporting industrial machinery and electronics without harming them.

The strong, lightweight polystyrene foam can be molded into various shapes to protect sensitive products like electronics, toys, and medical equipment.

Other Applications of molded EPS:

EPS has mechanical properties capable of being shaped in various ways. Some applications are as follows:

  • Chairs 
  • Infant car seats 
  • Seating in Premium Cars 
  • Insulated Panels 

3. Construction:

EPS is highly utilized in the construction industry thanks to many features like insulation properties, bacterial and pest resistance, and closed-cell structure, allowing minimal water penetration.

The strength and durability make it a prime choice for the construction industry to utilize in multiple products, mainly for insulation panel systems in walls, roofs, floors, etc., floors in buildings, as flotation materials for marinas and aquariums, and as lightweight filling in railway construction.

Interesting Read – What is TPR Material? | The Defintive Guide

Expanded Polystyrene Vs. Extruded Polystyrene – 

Expanded Polystyrene Extruded Polystyrene
EPS is manufactured by expanding spherical beads in a mold utilizing heat and pressure to blend beads. The bead structure is closed-cell, yet there is some space between each bead.
XPS is manufactured in a continuous extrusion process that produces a corresponding ‘closed cell’ with each cell fully enclosed with each other by polystyrene walls
ESP beads are molded in large blocks, which are cut into sheets using hot-wire machines.
XPS is “extruded” into sheets. Polystyrene is blended with several additives and a blowing agent – Both will be melted together through a dye.
EPS’ blowing agent leaves the beads rapidly, resulting in the formation of thousands of thousands of cells of air.
XPS is often chosen over EPS for wet and moisture operations as it needs a higher water vapor diffusion resistance value.
EPS water absorption is minimal but still more than XPS, which reduces its performance and insulation power.
The compressive strength of XPS is greater than EPS resulting in less water absorption and better performance.

Chemical Formula – C8H8

chemcial Formula - EPS


Polystyrene Recyclability and its Effects on the Environment – 

recyclability of EPS

Unlike many other thermoplastic materials, Expanded Polystyrene is CFC and HCFC-free. It is made up of organic elements like carbon, oxygen, and hydrogen.

EPS is 100% recyclable material and can be recycled at any stage of its life cycle. The designated plastic resin identification code is 6.

EPS effects on the environment are minimal because of combined efforts taken by many companies and countries worldwide. EPS is non-toxic and doesn’t leach any substances into the groundwater. Its manufacturing process is almost pollution-free as it doesn’t excrete any residual waste and doesn’t use ozone-layer-depleting CFCs and HCFCs.

Engaging Read – What is LDPE? | Low-Density Polyethylene | The Complete Guide

FAQs – 

1. Is expanded polystyrene a good insulator?

Ans. Expanded polystyrene is an outstanding insulator, thanks to its structure. It comprises 90% air and has a lot of tiny air pockets as it is made from polystyrene beads.

2. Why is EPS used so much for food packaging applications?

Ans. The biggest reason is its lightweight. It is compromised of 90% of air, making it one of the lightest packaging materials. The lightweight helps keep the transportation costs low and keeps the fuel emissions at a minimum. The excellent shock-absorbing property also keeps the products safe.

3. What is the monomer structure of polystyrene?

Ans. Polstyrene is a vinyl monomer. Talking about its structure, it has a long hydrocarbon chain with a phenyl group joined with a carbon atom. Polystyrene is produced using free radical vinyl polymerization.

4. What are the products made from Styrofoam?

Ans. Most of the Styrofoam applications are seen in the food packaging industry. Thee includes food and drink holders, coffee cups, egg cartons, coolers, plates and bowls, and go-to boxes.

Suggested Read – 

The Takeaway – 

Expanded Polystyrene foam is highly versatile and can be utilized in many applications. Proper use of EPS can boost your profits, improve production and quality, and preserve our planet.

Feel free to share your reviews in the comment box.

Leave a Comment