Polyurethane (PU) is a family of plastics (polymers) formed when two liquid components, a polyol and an isocyanate, react with each other. By changing the type and ratio of the components, the same chemistry gives a soft cushion foam, a rigid insulation foam, a flexible coating or a tough moulded part. That is why a mattress foam, a cold room panel and a refrigerator's insulation all come from the same family of materials.
Contents
1. How polyurethane forms
Polyurethane is made from two main raw materials: a polyol and an isocyanate. A polyol is a molecule carrying two or more hydroxyl (OH) groups. The isocyanate is most often MDI or TDI and carries two or more reactive NCO groups. When the two are mixed, a heat-releasing reaction starts and forms urethane bonds that link the molecules together. The polymer takes its name from this bond.
A two-component system: component A and component B
In industry, polyurethane is usually supplied as a two-component system. In Europe and Türkiye, component A is usually the ready blend of the polyol with catalysts, surfactants, blowing agents and other additives, and component B is the isocyanate matched to that blend. In North America the letters are often used the other way round, so always follow the labels on the drums and data sheets. A metering machine mixes the two at a set ratio and feeds the mix into a mould, onto a panel line or straight onto the surface being insulated.
How the foam forms
Two reactions run at the same time when a foam is made. In the gelling reaction, the polyol and the isocyanate build the polymer network. In the blowing reaction, the isocyanate reacts with water and releases carbon dioxide. This gas, together with any physical blowing agent in the system (pentane or HFO, for example), turns the liquid mix into a foam. The balance between the two reactions sets the cell structure and the density of the foam. The amine formed in the blowing reaction reacts with more isocyanate and forms urea links, so most foams contain some urea groups next to the urethane groups.
Why one chemistry gives so many products
Long, flexible polyol chains give soft products that spring back. Short, highly branched polyols build a tightly crosslinked, rigid structure. Small changes in the formulation directly change the density, hardness, insulation value and curing time. This is why polyurethane is spoken of as a system adjusted to each application rather than as a single product. Our guide Polyol and Isocyanate explains the two raw materials in more detail.
A short history
Polyurethane was first made in 1937 by Otto Bayer and his co-workers at IG Farben in Leverkusen, Germany. It was used on a small scale during the Second World War, for example as an aircraft coating, and rigid foams, elastomers, adhesives and flexible foams came into wider use in the 1950s. Today it is one of the major plastics: global production was about 25 million tonnes in 2019, around 6 percent of all polymers.
2. Types of polyurethane
In everyday speech, "polyurethane" usually means either a cushion foam or an insulation foam. The same chemistry, however, covers very different product groups:
Flexible polyurethane foam (cushion foam)
An open-cell, soft foam that springs back after compression, used in furniture, mattresses and car seats. It is either poured as large blocks (slabstock) and cut, or shaped in a mould. Depending on the application, its density ranges from about 10 to 300 kg/m³.
Flexible foam is made with polyether or polyester polyols. In general, polyether types resist water better, while polyester types resist solvents and abrasion better. Density, called "dansite" in the Turkish trade, is the mass of foam per cubic metre (kg/m³). On its own it does not describe firmness, because hardness is measured separately (for example by indentation, ISO 2439), so two foams of the same density can feel different.
Viscoelastic (memory) foam
A flexible foam that recovers slowly after it is pressed. Because it follows the shape of the body, it is used in mattresses, pillows and medical cushions.
Rigid polyurethane foam: PUR and PIR
A mostly closed-cell, light foam with high insulation value. It is used in sandwich panels, cold room panels, refrigerators, refrigerated truck bodies and hot water tanks. PIR (polyisocyanurate) is a rigid foam made with extra isocyanate that forms ring structures and is more stable under heat. The two differ in the ratio of isocyanate to polyol (the index): PUR is made at an index near 100, PIR at a much higher one, typically above 180. The name alone does not give a fire class; that comes from the product's classification report. Our guide PIR vs PUR compares the two.
Spray polyurethane foam
The two components are sprayed on site with a special machine and the foam rises within seconds. On roofs, facades and storage buildings it forms a continuous insulation layer with few or no joints.
Integral skin foam
A system that forms a dense outer skin and a lighter foam core in a single pour inside the mould. It is used for steering wheels, armrests, furniture parts and decorative products.
Elastomers, coatings and adhesives
Polyurethane is also used in forms that are not foams: wear-resistant elastomer parts such as wheels and rollers, floor and surface coatings, adhesives and sealants. Thermoplastic polyurethane (TPU), which can be reshaped with heat, belongs to the same family.
Polyurethane and polyurea: the difference
Polyurethane forms when an isocyanate reacts with a polyol; polyurea forms when an isocyanate reacts with an amine. Polyurea cures very fast and is usually applied with hot, high-pressure spray machines for waterproofing and protective coatings. Hybrid systems that combine the two also exist. See Spray Foam or Polyurea? for how applicators choose.
Is the foam in a can also polyurethane?
Yes. Most of the foam cans sold in hardware stores are one-component polyurethane foams that cure with the moisture in the air. They are different from the two-component systems industry uses to make panels, cushion foams and moulded parts. Uncured can foam contains reactive isocyanate, so wear gloves and eye protection, ventilate the room and follow the warnings on the can.
| Type | Cell structure | Typical use |
|---|---|---|
| Flexible foam | Open cell | Furniture, mattresses, seats |
| Viscoelastic foam | Open cell | Mattresses, pillows, medical cushions |
| Rigid foam (PUR/PIR) | Closed cell | Panels, cold rooms, refrigerators |
| Spray foam | Closed or open cell, by system | Roofs, facades, storage buildings |
| Integral skin foam | Dense skin, foam core | Steering wheels, armrests, decorative parts |
| Polyurea (related material) | Solid coating, not a foam | Waterproofing, protective coatings |
3. Main properties
The properties of polyurethane depend on its type, density and formulation, so each point below applies to the product group named in it:
- Thermal insulation: closed-cell rigid polyurethane is among the common insulation materials with the lowest thermal conductivity. PU Europe, the association of the European polyurethane (PUR/PIR) insulation industry, states that faced rigid polyurethane insulation can reach a thermal conductivity (λ) as low as 0.022 to 0.028 W/mK, depending on facings and thickness. The lower the λ, the less heat passes through, so the same insulation needs a thinner layer. This is an industry range, not the declared value of any single product.
- Light weight and strength: according to PU Europe, around 97 percent of the volume of rigid polyurethane foam is trapped gas, which is why it is so light. Its mechanical strength rises with density. In a sandwich panel it bonds firmly to the metal facings and forms the core that holds the panel together.
- Water and moisture: closed-cell rigid foam takes up almost no water, while open-cell flexible foam soaks it up. Water vapour permeability differs from product to product, so check the value on the technical data sheet.
- Heat and sunlight: heat resistance depends on the product, so no single figure applies to all polyurethane. Polyurethanes made with aromatic isocyanates yellow in sunlight and should not be left exposed without protection; coatings that must keep their colour use aliphatic systems.
- Service life: PU Europe states that rigid polyurethane foam has a useful life of 50 years and more, and ISOPA gives more than 50 years for building insulation. These are industry statements, not a guarantee for any single product.
4. What is polyurethane used for?
In short, polyurethane insulates buildings, cold rooms and refrigerators, cushions furniture, mattresses and car seats, and is used in coatings, adhesives and many moulded parts.
| Sector | Type used | Examples |
|---|---|---|
| Construction and insulation | Rigid foam, spray foam | Sandwich panels, roof and facade insulation |
| Cold chain | Rigid foam | Cold room panels, refrigerated truck bodies |
| Appliances | Rigid foam | Refrigerators, freezers, hot water tanks |
| Furniture and bedding | Flexible and viscoelastic foam | Sofas, mattresses, pillows |
| Automotive | Flexible and integral skin foam | Seats, armrests, steering wheels |
| Decoration | Rigid foam | Cornices, ceiling medallions, wood-look parts |
| Waterproofing and coatings | Polyurea, polyurethane coatings | Roofs, terraces, tank linings |
For moulded parts, a mould release agent helps the part come out of the mould cleanly. JiTPOL supplies systems for insulation, cushion foam, integral skin and spray applications: see our rigid, flexible, viscoelastic, integral skin and spray systems.
5. Is polyurethane harmful?
The answer depends on whether we mean the finished product or the raw materials.
The cured, finished product
According to the material information sheet of EUROPUR, the European association of flexible polyurethane foam block manufacturers, cured flexible polyurethane foam is classed as an article rather than a hazardous substance, and no effects on the skin or breathing are known in normal use. Suitable protection should still be used against the dust produced when the foam is cut or sanded, and gloves when working with freshly made foam. This statement is about flexible foam; for rigid foam, spray foam and other polyurethane products, check the product's own data sheets.
Raw materials and the people who process them
Isocyanates, the raw material, can cause allergic sensitisation of the skin and the airways. They should be handled by trained people, in well-ventilated areas and with suitable personal protective equipment. In the European Union, Regulation (EU) 2020/1149 requires industrial and professional users of products containing 0.1 percent by weight or more of diisocyanates to complete training before use; this has applied since 24 August 2023, and the training must be renewed at least every five years. Always read the safety data sheet (SDS) of each product.
Burning
Burning polyurethane releases dense smoke and toxic gases, so polyurethane waste should never be burned in the open.
6. Does polyurethane burn?
Yes, polyurethane is a combustible material. How it behaves in a fire depends on the product type, its density, whether it contains flame retardants and how it is built into the panel or wall. In Europe, the reaction-to-fire class of a construction product is determined by tests and classified under EN 13501-1; it is stated in the product's classification report and declaration of performance. Rely on those documents, not on general phrases such as "fireproof polyurethane". Terms such as "flame retarded" often refer only to small-scale ignition tests and do not describe the hazard in a large fire.
7. Polyurethane and other insulation materials
Compared with EPS (expanded polystyrene), XPS and stone wool, the clearest difference of rigid polyurethane is that its low thermal conductivity delivers the same insulation with a thinner layer. Where thickness and weight matter, as in panels and cold rooms, this difference decides the choice. Stone wool, on the other hand, is generally classed as non-combustible (Euroclass A1 or A2; check the product's declaration of performance) and may be preferred where the fire class comes first. The right choice depends on the required insulation value, the thickness, the moisture conditions, the fire requirements and the budget; compare each material by its own declared λ value.
8. Environment and recycling
Most polyurethane is a thermoset: its crosslinked structure means it cannot be melted and reshaped (thermoplastic polyurethane, TPU, is the exception), so it is harder to recycle than thermoplastics, but it can be recycled. Flexible foam offcuts are shredded and bonded again (rebonded) into products such as carpet underlay. Chemical methods such as glycolysis break the foam down into a polyol-rich product that can partly replace new polyol. Waste that cannot be recycled can go to energy recovery in controlled incineration with filtered emissions; burning it in the open is never acceptable. According to ISOPA, recycling rates remain low because of limited facilities and high costs. In insulation foams, the blowing agents that harmed the ozone layer (first CFCs, then HCFCs) have been phased out; in Europe they were replaced mainly by pentane, and some systems use HFO-type agents. For details, see our guide Polyurethane Recycling Methods.
9. How to choose the right system
Which polyurethane to use depends on the product you make and how you make it. These questions lead to the right system:
- What is the product, and what does it need: insulation, hardness, comfort or strength?
- What is the production method: continuous panel line, mould pouring, slabstock, injection or spray?
- Which density and curing time are needed?
- Which surfaces must the foam bond to, and under which conditions will it be produced?
- Which fire class, test or certificate is required?
Companies that develop ready two-component blends to answer these questions are called system houses. JiTPOL is a polyurethane system house in Bursa that develops and supplies such systems. We can help with system selection and send the technical data sheet (TDS) and safety data sheet (SDS) you need.
Frequently asked questions
Is polyurethane a plastic?
Yes. Polyurethane is a family of plastics (polymers). Most types are thermosets that do not melt when heated; some, such as thermoplastic polyurethane (TPU), can be shaped with heat.
Is polyurethane harmful?
Cured flexible foam is not treated as a hazardous substance in normal use. The raw material isocyanates can cause sensitisation, so they must be handled by trained people with protective equipment. See the product's safety data sheet (SDS) for details.
Does polyurethane burn?
Yes, it is combustible and produces dense smoke when it burns. Its fire class depends on the product, its density and any flame retardant, and is stated in the product's test report.
Does polyurethane yellow in sunlight?
Polyurethanes made with aromatic isocyanates, which includes most foams, change colour and turn yellow in sunlight. For flexible foam, EUROPUR states that this affects the surface colour, not the physical properties. Exposed rigid and spray foams should be covered or coated as their data sheet says; coatings that must keep their colour use aliphatic isocyanates.
Does polyurethane absorb water?
Closed-cell rigid foam takes up almost no water, while open-cell flexible foam soaks it up. For water vapour permeability, check the product's technical data sheet.
What is the difference between polyurethane and polyurea?
Polyurethane forms from an isocyanate and a polyol; polyurea forms from an isocyanate and an amine. Polyurea cures much faster and is usually applied with hot, high-pressure spray machines.
Is polyurethane foam the same as cushion foam?
Cushion foam is the everyday name for flexible, open-cell polyurethane foam. Rigid polyurethane foam is a closed-cell insulation material. Both come from the same chemistry but are different products.
Does polyurethane insulate better than EPS?
Rigid polyurethane has a lower thermal conductivity, so it gives the same insulation with a thinner layer. The choice also depends on thickness, fire requirements, moisture conditions and budget.
Can polyurethane be recycled?
Yes, although it is harder than for thermoplastics, and recycling rates remain low. Flexible foam offcuts can be shredded and bonded again into new products; chemical methods and controlled energy recovery are also used.
Sources
- ISOPA: What is polyurethane?
- ISOPA: Polyurethane FAQs
- PU Europe: polyurethane insulation
- EUROPUR: material information sheet, flexible polyurethane foam
- ISOPA fact sheet: rebonded flexible foam
- Wikipedia: Polyurethane
- OSHA: isocyanate hazards
- Commission Regulation (EU) 2020/1149 (diisocyanates, REACH Annex XVII)