The Whats and Hows of Expanded Polystyrene (EPS)

Feeling the squeeze from rising energy bills? Gas prices have gone through the roof, and end-users are the ones covering the markup. Households are spending substantially more to keep homes warm than just a few years ago. Blame the global gas shortage and the fact that many homes in the UK have insufficient levels of insulation. Tepid government schemes haven’t helped either.  

Contrary to what most people believe, keeping warmth in doesn’t have to cost much. Insulating your home costs less than any other energy investment, and owners benefit as soon as it is installed. There are dozens of inexpensive insulation products, like fiberglass rolls, batts, and foam boards in various configurations to keep energy bills at bay. These can be used for different purposes when insulating homes and businesses. And the best part is you can do all the work yourself.  

What is Expanded Polystyrene? 

One low-cost option for energy efficiency and better comfort levels is Expanded Polystyrene or EPS. This is a rigid thermoplastic foam that has been used extensively for insulation purposes since the 1950s. It has a closed-cell structure, meaning good thermal properties, high impact resistance, and low water vapor permeance. It is used as foam block or boards in walls, floors, and roofs for residential and commercial properties.  

How is EPS Made?  

EPS is made from polystyrene beads in several stages. The small beads are first softened by steam and a blowing agent, pentane or hexane, expands the beads by up to 40 times their original size. This is then sent to silos for aging, with air replacing the blowing agent. The pre-foam product then goes into a mould for additional steaming, and it is here that the beads fuse together into a block. The block is then dried in an oven and then cut to shape.  

The thermal and insulative properties of EPS depend on the density and thickness. Low and standard density EPS blocks are sold as EPS 50 and EPS 70, respectively. High density, or 100 EPS, is the middle ground and is widely used for domestic purposes. It has a density of 20 kilos per cubic meter. Large-scale projects can benefit from ultra-high density EPS, marketed as either EPS 150 or EPS 200.  


EPS is used for a variety of insulative applications. It is found in cavity wall insulation, floor insulation (especially concrete floors), attic and loft applications, insulation of external walls and piping, and more. Besides insulation, it is also found in decorative tiles and mouldings as well as vinyl siding. Good structural rigidity means EPS can be used in laminated walkway boards. Outside of construction, EPS is widely used in packaging for its high shock-absorbing qualities.  

Benefits of EPS 

EPS is the insulation material of choice because of a host of properties that go in its favor. 

• Cost-Effective 

EPS offers the best price/performance ratio among all rigid insulation products currently available. For example, to achieve the same thermal properties provided by a 100 mm thick PIR board, you would need to specify an EPS foam board of 135 mm. This works out at roughly half the price. For large-scale projects where space is available, the savings pile up.  

• Thermal Properties 

Expanded polystyrene has favorable thermal properties due to the closed-cell structure, consisting of 98% air. The trapped air in the cells is a poor heat conductor. The thermal conductivity of 100 EPS specified in 10 cm is 0.037 Watts per meter times Kelvin, or in plain speak, equal to that of a 300 cm solid brick wall.  

• Lightweight 

Since it contains mostly air, EPS boards and blocks are extremely light. EPS in lower densities is lighter than that in higher densities. All variants though are easy to work with, so transporting them to or within the workplace is a breeze, literally.  

• Durability 

EPS doesn’t decompose and will retain form during the lifetime of the building. It won’t off-gas like PIR, for instance. In addition, it doesn’t attract insects or vermin. 

• Strength 

This is owed to the closed-cell structure. EPS has high compressive strength and rigidity, meeting British and EU construction standards. Overall strength increases with density and thickness. High strength means it is the preferred choice in flooring applications.  

• Moisture Management and Water Resistance 

Expanded polystyrene allows humidity generated indoors to escape, preventing the buildup of mould and mildew. In addition, the closed-cell structure, combined with permeable film facers, eliminates outside water absorption, so walls remain dry.  

• Fire Resistance 

EPS is combustible and melts at 360 °C. This, though, can be offset with the use of flame retardant additives, that prevent the material from igniting when subjected to higher heat. In addition, metallic facers and gypsum fire barriers can prevent the spread of flames, in what is known as self-extinguishing EPS. Any smoke or particles are non-toxic.  

• Eco-friendliness 

Compared to other insulation materials, EPS contains no CFCs, so there’s no ozone depletion. It is also 100 percent recyclable, and any unused or damaged pieces can be re-formed. EPS is also safe to use, being non-toxic, odorless and doesn’t contain skin or respiratory irritants (mineral wool, anyone?) 

• Quick and Easy Installation 

EPS is light, practical, and easy to cut to shape and size with basic tools.  

• Versatility 

EPS can be manufactured in standard board sizes (1200 by 2400 mm) or produced in any shape and size needed. It is also flexible and compatible with a wide variety of building materials and is used in many applications.  

Compared to Other Insulation Materials 

Compared to its closest sibling, Extruded Polystyrene (XPS), EPS is cheaper and retains considerably less moisture. It also has comparable compressive strength. However, it has somewhat lower thermal efficiency (or R) values, though it can be specified in thicker and denser boards in places like concrete slab flooring or exterior walls for much less. Compared to more expensive options like PU/PIR boards, EPS has lower fire resistance, slightly less strength, and lower efficiency ratings. But with PIR boards coming in at 2 or 3 times the cost (depending on thickness), those advantages soon start to fade. 

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