Flexible foam raw materials are the liquid chemicals that form flexible polyurethane foam: a polyol, an isocyanate (mostly TDI) and water, plus catalysts, a surfactant and other additives when needed. The mix is foamed as a large block (slabstock) or inside a mould. The right system depends on the product you make, the target density and hardness, the foam type (conventional, HR, memory) and your production method.
Contents
- 1. What are flexible foam raw materials?
- 2. What is flexible polyurethane foam made of?
- 3. How is flexible foam made?
- 4. What is slabstock? Slabstock and moulded foam
- 5. Types of flexible foam: conventional, HR, memory, rebonded
- 6. What is memory foam? (viscoelastic foam)
- 7. What does density mean? How it differs from hardness
- 8. How to choose flexible foam raw materials by application
- 9. What to tell the supplier when you specify flexible foam raw materials
- Frequently asked questions
1. What are flexible foam raw materials?
Flexible polyurethane foam (PU foam) is the soft material inside sofa cushions, mattresses and car seats. The foam is generally open-cell, so air can flow through it, and it springs back when a load is removed. The liquid chemicals it is made from are its raw materials. The wider picture is in our guides "What Is Polyurethane?" and "What Is Polyurethane Foam?".
This guide is about those liquid chemicals. The finished foam block that is cut and upholstered is the product made from them; Section 4 explains how that block is made. Cleaning sponges are outside the scope of this guide.
2. What is flexible polyurethane foam made of?
According to the material information sheet of EUROPUR, the European association of flexible polyurethane foam block manufacturers, flexible foam forms from diisocyanates, polyols (a large share) and water (a small share), and additives are used in small concentrations. The table gives a general overview of each raw material and its role in the mix.
| Raw material | What it does | Role in the mix |
|---|---|---|
| Polyol (mostly polyether) | Forms the flexible polymer chains | Main component |
| Isocyanate (mostly TDI, sometimes MDI) | Reacts with the polyol and with water and builds the polymer network | Main component |
| Water | Reacts with the isocyanate and releases carbon dioxide, the gas that blows the foam | Minor component, small share |
| Catalysts | Speed up and balance the reactions | Small additive |
| Surfactant | Helps the foam form an even, stable cell structure | Small additive |
| Other additives (for example flame retardants, pigments) | Influence specific properties, for example flame resistance, or add colour | Small additive, only when needed |
Which additives are used, and how much of each, depends on the specification of the foam to be produced (EUROPUR).
Polyol: polyether and polyester
Polyether polyols are the more widely used type for flexible foam, and polyester polyols are less common in soft foams; EUROPUR lists both foam types. The polyol type is one of the factors that shape the properties of the finished foam.
Isocyanate: TDI and MDI
EUROPUR names TDI (toluene diisocyanate) as the main diisocyanate for flexible foam. Moulded foams are more often made with MDI (methylene diphenyl diisocyanate), and memory foam can also be made with MDI. For more detail, see our guide "Polyol and Isocyanate".
3. How is flexible foam made?
In flexible foam production, the liquid components are metered and mixed, and the mix then foams, rises and solidifies. The foaming comes from carbon dioxide, which is released when the isocyanate reacts with water, while the reaction of the polyol with the isocyanate builds the polymer that gives the foam its structure. The details depend on the system and on the production line.
Safety when handling the raw materials
Isocyanates can cause allergic sensitisation of the skin and airways, so they should be used by trained people with suitable protective equipment. In the EU, Regulation 2020/1149 requires industrial and professional users of products with 0.1 percent by weight or more of diisocyanates to be trained before use; this has applied since 24 August 2023 and the training must be renewed at least every five years. According to EUROPUR, the diisocyanates are consumed in the reaction, and cured flexible polyurethane foam is an article under REACH, not a hazardous product. That statement covers cured flexible foam only.
4. What is slabstock? Slabstock and moulded foam
Slabstock, or flexible slabstock foam, is flexible polyurethane foam made as a large, continuous block that is cut into shape afterwards. The mix is laid onto a moving conveyor, rises freely and solidifies, and the block is later cut into sheets, rolls or shaped parts. According to EUROPUR, most of the slabstock foam made in Europe goes into mattresses and furniture, and a smaller part into transportation.
Moulded (molded) flexible polyurethane foam is poured or injected into a closed mould, so the part comes out close to its final shape. This route can make shapes that are hard to cut from a block and can combine foam with parts such as a metal frame. Mould costs are high, so the US Polyurethane Foam Association (PFA) notes that moulding is typically reserved for high production runs. Almost all car seats in Europe are made of flexible moulded foam (EUROPUR). A mould release agent helps the part leave the mould cleanly. Moulded foam is made by hot cure or cold cure processes; today the dominant one worldwide is cold cure foam, also known as high resilience (HR) foam (Euromoulders).
| Feature | Slabstock (block) foam | Moulded foam |
|---|---|---|
| How it is made | Continuous line: the mix rises freely on a conveyor and the block is cut afterwards | The mix goes into a closed mould, one part at a time |
| Typical use | Mattresses, furniture cushions, packaging | Car seats, headrests, office furniture parts |
5. Types of flexible foam: conventional, HR, memory, rebonded
EUROPUR names three common families of flexible foam: standard ether, high resilience (HR) and visco-elastic. They differ in density, hardness, tensile strength and viscosity, among other properties. Rebonded foam, made from shredded foam scrap, is a separate product.
| Type | What it is | Typical use |
|---|---|---|
| Conventional (standard ether) | Basic cushioning foam; may lack long-term durability and resilience | Budget mattresses, base layers |
| HR (high resilience) | Higher resilience than conventional foam and generally better support and durability; made as slabstock and as moulded foam | Premium mattresses, seating, car seats |
| Memory (viscoelastic) | Recovers slowly, very low resilience, follows the body shape (see section 6) | Mattress and pillow layers, medical cushions |
| Rebonded | Shredded foam pieces pressed together with a binder (ISOPA) | Carpet underlay, sports mats, flooring, packaging |
For the difference between flexible and rigid foam, see "Rigid vs Flexible Polyurethane Systems"; for rebonded foam and recycling, see "Polyurethane Recycling Methods".
6. What is memory foam? (viscoelastic foam)
Memory foam (viscoelastic or "visco" foam) is a polyurethane foam that recovers slowly after it is pressed. It consists mainly of polyurethane with additional chemicals that increase its viscosity and density. Its cells are open and its resilience is very low. Its behaviour depends on temperature, and it typically softens with body heat. It was developed in 1966 under a NASA contract to improve the protection and comfort of airplane seats.
Memory foam is used in mattresses, pillows and medical cushions. A mattress often combines several types of foam in layers (EUROPUR). A memory foam mattress is usually denser, and therefore heavier, than other foam mattresses. For our systems, see "Viscoelastic Polyurethane: Memory Foam Systems" and "Memory Foam Systems for Mattresses & Pillows".
7. What does density mean? How it differs from hardness
Density is the mass of foam per cubic metre, in kg/m³. According to PFA it indicates comfort, support, durability and cost: higher density foam generally keeps its properties longer but uses more material and costs more. Flexible foam is made over a very wide range of densities, depending on the type and the application.
Hardness is a separate property: it is measured by the force needed to press the foam by a given amount. Standardised test methods such as ISO 2439 or ASTM D3574 are used.
What sets the hardness at a given density?
Density and hardness are set independently: PFA states that a high density foam can be soft and a low density foam can be firm. Hardness is shaped by the formulation, the foam type and other factors, and a hardness value means little without the test method it was measured with.
| Property | What it is | Why it matters |
|---|---|---|
| Density (kg/m³) | Mass of foam per cubic metre | Indicates durability, support and cost |
| Hardness | Force needed to press the foam by a given amount | How the foam feels when you sit or lie on it |
| Resilience | How much the foam springs back | Linked to comfort; very low in memory foam |
| Compression set | Permanent loss of height after the foam has been compressed | Durability in use, for example body impressions on a mattress |
8. How to choose flexible foam raw materials by application
Start with the product. Most of the flexible foam made in Europe goes into bedding and upholstery (EUROPUR), but each application asks for something different.
| Application | What matters most | Usual foam type and method |
|---|---|---|
| Furniture cushions | Support, comfort, durability, fire safety requirements | Conventional or HR; slabstock cut to shape, or moulded |
| Mattresses | Support, comfort, durability, emission and fire safety requirements | Conventional, HR and memory foam, often in layers; slabstock |
| Car seats | Comfort, durability under repeated loading, fire and emission requirements for vehicle interiors | HR (cold cure), moulded |
| Packaging | Shock absorption, a shape that fits the packed item | Slabstock cut to shape |
The right density and hardness depend on the product, the load it carries and the foam type. They are best set together with the foam supplier, who needs to know the use and the production method (see section 9).
Choosing by production method
A continuous slabstock line and a moulding line use different systems, so the production method is part of the choice. A system house formulates the blend to suit your process and production line, and our technical team supports you with this. For seating, see Cold-Cure & Slabstock Foam Systems for Seating; for all flexible systems, see Flexible Polyurethane Foam Systems.
9. What to tell the supplier when you specify flexible foam raw materials
Foam makers buy raw materials in two ways: separately (polyol, isocyanate and additives) to build their own recipe, or as a matched ready system from a system house. A ready system usually has two components: A is the polyol blend and B is the isocyanate. This is the usage in Türkiye and Europe; in North America the letters are often reversed, so follow the drum labels. The buying options are covered in our guide Buying Polyurethane Systems from Türkiye. JiTPOL is a polyurethane system house in Bursa that develops and supplies flexible, viscoelastic and other systems.
Whichever supplier you ask, give this information:
| What to tell the supplier | Why it matters |
|---|---|
| Product and use: cushion, mattress layer, car seat or packaging | It sets the foam type and the range of density and hardness |
| Production method and equipment: slabstock line or mould | The system has to match the processing conditions of your line |
| Target density and hardness, and how they are measured | The same density can be soft or firm, and values from different methods cannot be compared directly |
| Foam type: conventional, HR or memory | It sets resilience and durability |
| Fire and emission requirements of your target market | Foam is combustible (EUROPUR). Fire tests apply to the finished product, for example foam with its cover, and "flame retarded" alone is not a fire class |
| Monthly volume, packaging and documents (technical data sheet, safety data sheet) | It allows a supply plan and a safe handling check |
Frequently asked questions
What are the raw materials of flexible foam?
Flexible polyurethane foam (PU foam) is made from a polyol, an isocyanate (mostly TDI) and water, plus catalysts, a surfactant and, when needed, additives such as flame retardants or pigments. Most of the mix is polyol and isocyanate.
How is flexible foam made?
The components are metered and mixed, and the mix foams, rises and solidifies. The foaming comes from carbon dioxide released when the isocyanate reacts with water. Slabstock foam is made as a large block on a continuous line and cut afterwards; moulded foam is poured into a closed mould and comes out close to its final shape.
What does density mean for foam?
Density is the mass of foam per cubic metre (kg/m³). According to PFA it indicates durability, support and cost, but it does not set hardness: a high density foam can be soft and a low density foam can be firm. Hardness is measured separately, for example with ISO 2439.
What is memory foam (visco foam)?
Memory foam is a viscoelastic polyurethane foam that recovers slowly after it is pressed. Its resilience is very low, its behaviour depends on temperature and it typically softens with body heat. It was developed in 1966 under a NASA contract to improve the protection and comfort of airplane seats, and it is used in mattresses, pillows and medical cushions. It can be made with TDI or MDI.
What is HR foam?
HR stands for high resilience. HR foam has a higher resilience than conventional foam and generally better support and durability. Cold cure moulded foam, today the dominant moulding process worldwide, is also called HR foam, and HR foam is made as slabstock as well. It is used in car seats, premium mattresses and upholstered furniture.
What is the difference between slabstock and moulded foam?
Slabstock foam is made as a large block on a continuous line and then cut into sheets or shaped parts; it is common in mattresses and furniture. Moulded foam is made for each part in a closed mould and comes out close to its final shape. Moulds are costly, so moulding is mostly used for high volumes such as car seats.
What density of foam should be used for furniture?
There is no single right value. The right density depends on the product, the load it carries, the foam type and the expected service life; higher density generally lasts longer but costs more. Set the target together with your foam supplier. The JiTPOL technical team can help you with this, and the technical data sheet of the chosen system gives the details.
Sources
- EUROPUR: Flexible PU foam FAQ
- EUROPUR: Raw materials
- EUROPUR: What is polyurethane foam?
- EUROPUR: material information sheet, flexible polyurethane foam
- EUROPUR: Flexible polyurethane foam for mattresses
- PFA: What is polyurethane foam?
- PFA: Foam performance
- PFA: Furniture case study
- PCC: Polyols for flexible foams
- PFA bulletin: The importance of density
- PFA bulletin: Foam test methods and flammability tests
- Euromoulders: Moulded polyurethane
- ISOPA fact sheet: rebonded flexible foam
- Wikipedia: Polyurethane
- Wikipedia: Memory foam
- NASA Spinoff 2005: Forty-Year-Old Foam Springs Back With New Benefits
- ISO 2439:2008: Determination of hardness (indentation technique)
- Efectis: Furniture flammability test methods
- Commission Regulation (EU) 2020/1149 (diisocyanates, REACH Annex XVII)