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Foam properties are the physical, chemical, thermal and acoustic characteristics that decide how a foam performs and which jobs it suits. Foam is a material formed by trapping pockets of gas in a liquid or solid, and these pockets, or cells, give foam its distinctive properties.
From packaging and insulation to furniture and mattresses, foam products are everywhere in daily life. This guide explains the main properties of foam and how they affect the performance of foam products.
| Property Group | Includes | What It Affects |
|---|---|---|
| Physical | Density, hardness, resilience | Durability, comfort and support |
| Chemical | Flammability, chemical resistance, biodegradability | Safety, durability and environmental impact |
| Thermal | Thermal conductivity, thermal expansion, heat resistance | Insulation performance and high-temperature use |
| Acoustic | Sound absorption, sound insulation | Soundproofing, acoustics and noise reduction |
The physical properties of foam include its density, hardness and resilience. They are determined by the size and distribution of the foam’s cells and the material the foam is made from, and they play a crucial role in deciding which applications a foam suits.
For instance, high-density foam, which has more material and less air per cubic metre, is typically more durable and gives better support in applications such as mattresses and furniture. Low-density foam is lighter and less expensive, making it suitable for packaging and other lightweight applications.
Density is the amount of material in a given volume of foam. In the UK it is measured in kilograms per cubic metre (kg/m3); in the US, pounds per cubic foot (PCF) is common. Density affects a foam’s durability, comfort and support: high-density foam tends to be more durable and supportive, but it can also be heavier and more expensive than low-density foam. See our guide to foam density.
Density depends on how much polymer material is used in a given volume during production, and can also be affected by the size and distribution of the foam’s cells.
Hardness is how firm or soft a foam is. For flexible foams it is usually measured with an indentation test, such as Indentation Load Deflection (ILD), which records the force needed to compress a sample by a set amount; a durometer, which measures resistance to indentation, is used for some firmer foams. Hardness affects the comfort, support and durability of foam products. See our guides to foam compression and foam testing.
Hardness depends on the type of polymer, the foam’s formulation and its cell structure, and it can be adjusted during manufacturing. Density and hardness are separate properties: a high-density foam can be made soft or firm, so it is worth checking both.
The chemical properties of foam include its flammability, resistance to chemicals and biodegradability. They are determined by the type of polymer used and any additives or treatments applied to the foam.
For instance, some foams are treated with flame retardants to reduce their flammability, while others are treated with antimicrobial agents to resist bacteria and mould. These properties can significantly affect a foam’s safety, durability and environmental impact. See also our guide to foam recycling.
Flammability is how easily a foam catches fire and keeps burning. It is a critical property for applications in close contact with people, such as furniture, mattresses and insulation.
Flammability depends on the polymer and any flame retardants or other additives used. Some polymers, such as polyurethane, are naturally flammable, while others, such as silicone, are naturally flame-resistant. Most foams used in commercial applications are therefore treated or formulated to meet safety standards; in the UK, foam in upholstered furniture must meet the Furniture and Furnishings (Fire) (Safety) Regulations 1988.
Chemical resistance is a foam’s ability to withstand exposure to chemicals without degrading or losing its properties. It is important for foams used in industrial applications, where they may come into contact with oils, solvents and other chemicals.
Chemical resistance depends on the polymer and any chemical-resistant treatments or coatings. For instance, polyethylene foam is naturally resistant to many chemicals, while polyurethane foam is more easily affected by some solvents and may need a protective coating.
The thermal properties of foam include its thermal conductivity, thermal expansion and heat resistance. They are determined by the polymer used and the size and distribution of the foam’s cells.
For instance, foams with small, closed cells tend to have low thermal conductivity, making them excellent insulators. Foams with larger, open cells generally conduct heat more readily, so they insulate less effectively.
Thermal conductivity is a foam’s ability to conduct heat. It is a crucial property for insulation, where low thermal conductivity is needed to reduce heat transfer.
Thermal conductivity depends on the polymer and the size and distribution of the cells. Rigid closed-cell foams, such as rigid polyurethane foam and polystyrene, have low thermal conductivity, while flexible open-cell foams conduct heat more readily.
Heat resistance is a foam’s ability to withstand high temperatures without degrading or losing its properties. It is important for foams used in high-temperature applications, such as insulation for hot water pipes or electronics packaging.
Heat resistance depends on the polymer and any heat-resistant treatments or coatings. For instance, silicone foam is naturally heat-resistant, while standard polyurethane foam has a lower maximum working temperature.
The acoustic properties of foam include sound absorption and sound insulation. They are determined by the size and distribution of the foam’s cells and the material the foam is made from.
For instance, open-cell foams are good at absorbing sound, making them ideal for acoustic treatment. Closed-cell foams are better than open-cell foams at blocking sound, making them useful for noise reduction and sound isolation.
Sound absorption is a foam’s ability to absorb sound waves, reducing their intensity and stopping them reflecting back into a room. High sound absorption is needed in acoustic treatment to reduce echo and noise levels.
Open-cell foams, such as flexible polyurethane and melamine foam, absorb sound well, while closed-cell foams, such as polyethylene and polystyrene foam, are less effective.
Sound insulation is a foam’s ability to stop sound waves passing through it. It matters for noise reduction and sound isolation, where the aim is to prevent noise transmission.
Closed-cell foams, such as polyethylene and polystyrene foam, insulate sound better than open-cell foams such as polyurethane and melamine foam. Because foam is light, it is usually combined with denser materials where high sound insulation is needed.
Understanding the properties of foam is key to choosing the right foam product for a particular application. Whether it is for insulation, packaging, furniture or soundproofing, the physical, chemical, thermal and acoustic properties of foam all play a part in its performance and suitability.
By considering these properties, manufacturers can design foam products that meet specific requirements and standards for safety, durability and effectiveness, and consumers can make informed choices about the foam products they use. See our guide to foam manufacturing for how these properties are built in.
Continue exploring foam specifications, performance and fabrication methods across our technical library:
Balancing density, firmness and resilience is the key to seating that stays comfortable for years. Whether you are cutting replacement sofa cushions, ordering custom window seat foam or planning an upholstery project, the Foam & Covers team can help you choose the right foam grade and cut it precisely to size.
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