What is Polystyrene Insulation?

Adam Hill

Polystyrene insulation is a type of rigid foam insulation which is commonly used in residential and commercial settings. It has an exceptional ability to insulate against noise and extreme temperatures. It is also waterproof and long-lasting. These qualities combine to make polystyrene insulation an exceptionally useful product.

Polystyrene foam is used to make insulation commonly found in homes.
Polystyrene foam is used to make insulation commonly found in homes.

Two types of polystyrene are used for insulation: expanded and extruded polystyrene. Expanded polystyrene, also called bead board, has a lower density that the extruded kind, and is less expensive, but also has slightly less insulating power. This is because of its coarse cells and the fact that they contain only air. Extruded polystyrene insulation has finer cells or beads, and contains a mixture of air and refrigerant gas, making it a better insulator.

Polystyrene insulation can be used in residential or commercial buildings.
Polystyrene insulation can be used in residential or commercial buildings.

Extruded polystyrene, due to the way in which it is made, has other qualities that make it a superior choice for insulation. It begins in the form of solid polystyrene crystals, which are combined with special additives and melted. In an extruder, the temperature and pressure are tightly controlled to convert the crystals into a thick plastic fluid. This liquid is then forced into a mold or die. Upon emerging from the die, it cools and expands into a foam, which can be cut or shaped to any specifications.

This process gives extruded polystyrene insulation a smooth, uniform surface which is impossible to duplicate in other types of insulation. Its qualities also make it well-suited for formation into panels or stackable blocks for the purpose of wall insulation in homes. The foam can easily be cut for electrical wiring to be run through or near it. These interlocking foam formations are often made with hollow regions that can be filled with concrete which creates a grid of columns and beams when dry.

The materials for polystyrene insulation are often quite expensive and can add approximately five to ten percent onto the cost of building a house. However, the savings on heating and cooling can allow the homeowner to recoup the extra cost over the life of the structure. The concrete grid in the insulation offers its own benefits apart from the polystyrene. These include being impervious to many pests such as termites that can cause structural damage to an ordinary wood frame home if left unchecked.

As with any alternative building material, polystyrene insulation does have some disadvantages. Apart from the increased cost, it is also flammable and requires a fire-protective coating. It can also slightly degrade if exposed to sunlight or temperatures above 165 degrees Fahrenheit (74 degrees C). However, considering that most home insulation is never exposed to that type of temperature, it presents little practical risk.

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Discussion Comments


Polystyrene insulation in cladding is very useful product. It has many qualities, which makes it better than other insulation methods.


I don't want my house insulation to biodegrade!

Also, it's very difficult to install bales of straw under 2000 of single ply roofing membrane.


Refrigerant gas, additives? And extremely slow to biodegrade after use. Try straw or wool - true 'alternatives'.


Thank you, a very useful and interesting guide.

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