Polyurethane raw materials are the chemicals that react together to form polyurethane: a polyol and an isocyanate, plus a small set of additives that decide how fast the reaction runs, how the foam rises, how dense and how fire-resistant the final part is. The same two families of raw material make a mattress, a cold-room panel, a shoe sole and a floor coating; what changes is the exact grade of each component and the recipe that combines them.
Polyurethane is made by reacting polyols (polyether or polyester molecules with several OH groups) with isocyanates (mainly MDI or TDI). Additives such as amine and metal catalysts, silicone surfactants, blowing agents, flame retardants and chain extenders control the reaction and the properties of the finished foam, elastomer, coating or adhesive.
- Two core components: a polyol blend and an isocyanate react in a fixed ratio to form urethane links.
- MDI dominates rigid and moulded applications; TDI is used mainly for flexible slabstock foam.
- Additives are small in volume but decisive: a change of catalyst or surfactant can turn a good foam into a collapsed one.
- Every delivery should be checked against OH value, NCO content, viscosity and water content.
- Isocyanates need trained handling: in the EU, training is mandatory for most industrial and professional users since August 2023.
01What Are Polyurethane Raw Materials?
Polyurethane raw materials are the reactive chemicals and auxiliaries from which every polyurethane product is made. Unlike polyethylene or PVC, polyurethane is not delivered as a finished plastic to be melted and shaped: it is created on site, in the mould, the panel line or the spray gun, when liquid components are mixed and react within seconds or minutes.
The raw materials fall into three groups:
- Polyols provide the "soft" backbone of the polymer. Their molecular weight and number of OH groups (functionality) decide whether the result is a soft flexible foam, a tough elastomer or a hard insulation board. See the full guide to polyols for polyurethane.
- Isocyanates provide the reactive NCO groups that link the polyols together. Methylene diphenyl diisocyanate (MDI) and toluene diisocyanate (TDI) account for the vast majority of volume; aliphatic isocyanates serve light-stable coatings. See isocyanates: MDI, TDI and prepolymers.
- Additives are used in small amounts, often a few parts per hundred parts of polyol, but they steer everything else: reaction speed, cell size, blowing, fire performance, colour and demoulding. See polyurethane additives.
Manufacturers buy these materials in two ways. Large producers with in-house formulation expertise buy individual raw materials and blend their own recipe. Most converters buy a formulated system: a ready polyol blend that already contains the catalysts, surfactant, blowing agent and flame retardant, delivered together with the matching isocyanate. A company that develops and supplies such systems is called a systems house.
02How Polyurethane Is Made: The Core Reaction
Polyurethane forms when the isocyanate group (-N=C=O) of an isocyanate reacts with the hydroxyl group (-OH) of a polyol, creating a urethane link. Because both molecules carry two or more reactive groups, the links grow into a long chain or a three-dimensional network.
R-N=C=O + R'-OH → R-NH-CO-O-R' (urethane)
A second reaction matters just as much in foams. Isocyanate also reacts with water, releasing carbon dioxide gas and forming urea links. That gas is the "chemical" blowing agent that expands most flexible foams, which is why the water content of a polyol blend is tightly specified.
2 R-N=C=O + H2O → R-NH-CO-NH-R + CO2↑
- Polyol blendPolyols + catalysts, silicone surfactant, blowing agent, flame retardant, chain extender
- IsocyanatePolymeric or modified MDI, TDI, or an NCO-terminated prepolymer
- PolyurethaneRigid or flexible foam, elastomer, coating, adhesive, sealant or binder
The Isocyanate Index
The ratio between the two components is expressed as the isocyanate index: the amount of isocyanate actually used divided by the amount needed to react with every OH group (and water), multiplied by 100. An index of 100 is exact stoichiometry. Flexible foams typically run between about 100 and 115; elastomers and coatings close to 100-105; polyisocyanurate (PIR) insulation boards use a large excess, often an index of 250 or more, so that the surplus NCO groups trimerise into heat-stable isocyanurate rings.
03Polyols: The Backbone
Polyols are the largest raw material by volume in most formulations. Two chemical families cover almost every application.
- Polyether polyols are made by adding propylene oxide and ethylene oxide to an initiator. Glycerine-started triols of high molecular weight give flexible and HR moulded foams; short, highly functional polyols started on sucrose, sorbitol, amines or Mannich bases give rigid insulation foams.
- Polyester polyols are made by condensing acids such as adipic acid or phthalic anhydride with glycols. Saturated adipate polyesters give strength and abrasion resistance in shoe soles, elastomers and adhesives; aromatic polyester polyols, including grades made from recycled PET, are a staple of PIR and rigid foam.
- Polymer polyols contain finely dispersed styrene-acrylonitrile (SAN) particles that raise load-bearing and cell stability in flexible foam.
The most important specification is the hydroxyl value (OH value, mg KOH/g): low values (about 25-60) indicate long, flexible chains; high values (about 300-800) indicate short, rigid ones. Pluskim supplies both families, from glycerine-initiated HR polyols to its own PLUSTEROL polyester polyol series; the Pluskim polyol range lists the initiator types available. Read more in the polyols guide or the comparison polyether vs polyester polyols.
04Isocyanates: MDI, TDI And Prepolymers
Isocyanates are the reactive partner; their NCO content (the weight percentage of isocyanate groups) sets how much is needed per kilogram of polyol.
- Polymeric MDI (typically about 31 % NCO) is the workhorse of rigid foam: sandwich panels, spray foam, refrigerators, pipe insulation and binders.
- Monomeric and modified MDI serve elastomers, integral skin, shoe soles, adhesives and HR moulded foam, where processability and mechanical properties matter.
- TDI (typically about 48 % NCO, usually as an 80/20 isomer blend) is used mainly for flexible slabstock foam for furniture and mattresses.
- Prepolymers are isocyanates partly pre-reacted with polyol, leaving roughly 1-30 % free NCO. They give easier ratios, lower volatility and tailored properties in elastomers, coatings and adhesives.
The choice between MDI and TDI is covered in detail in MDI vs TDI. Pluskim supplies polymeric, monomeric and modified MDI as well as TDI, and offers MDI-based prepolymers under its PLUSNATE series; see Pluskim isocyanates.
05Additives: Small Doses, Decisive Effects
Additives make up a small fraction of a formulation by weight, yet they decide whether the reaction can run on a production line at all. The main groups are:
| Additive | What it does | Typical examples |
|---|---|---|
| Catalysts | Set the speed of the gelling (polyol-isocyanate) and blowing (water-isocyanate) reactions and their balance | Tertiary amines; tin, bismuth and potassium carboxylates |
| Silicone surfactants | Nucleate and stabilise cells, control open or closed cell structure | Polyether-polysiloxane copolymers |
| Blowing agents | Expand the foam to the target density | Water (CO2), pentanes, HFOs, methyl formate |
| Flame retardants | Improve fire performance to meet building and transport standards | TCPP, TEP, expandable graphite, reactive FRs |
| Chain extenders and crosslinkers | Build hard segments, raise hardness and crosslink density | MEG, DEG, 1,4-butanediol, glycerine |
| Fillers and plasticizers | Adjust density, cost, flexibility and processing | Glass microspheres, DOTP |
| Colorants and mould release | Colour the part and release it cleanly from the mould | Pigment pastes, wax- or soap-based release agents |
The additives guide gives typical dosages and a troubleshooting table that links common foam defects to their usual additive cause.
06Polyurethane Raw Material List
The table below lists the raw materials found in commercial polyurethane formulations, what each contributes and where it is mainly used. It is the quickest way to see which materials a given application needs.
| Raw material | Group | Role in the formulation | Main applications |
|---|---|---|---|
| Flexible polyether polyol (triol, MW about 3,000-6,000) | Polyol | Soft segment, elasticity | Slabstock, HR moulded and viscoelastic foam |
| Rigid polyether polyol (sucrose, sorbitol, amine, Mannich) | Polyol | High crosslink density, rigidity | Panels, spray foam, appliances, pipe insulation |
| Saturated polyester polyol (adipate) | Polyol | Strength, abrasion and oil resistance | Shoe soles, elastomers, adhesives, coatings |
| Aromatic polyester polyol (PA or recycled PET based) | Polyol | Fire performance, rigidity, recycled content | PIR boards, panels, spray foam |
| Polymer polyol (SAN-filled) | Polyol | Load-bearing, cell opening | Furniture and automotive seating foam |
| Polymeric MDI | Isocyanate | Crosslinking, rigid network | Rigid foam, binders, panels |
| Monomeric and modified MDI | Isocyanate | Linear hard segments, processability | Elastomers, soles, integral skin, adhesives |
| TDI 80/20 | Isocyanate | Reactive partner for flexible foam | Flexible slabstock foam |
| MDI or TDI prepolymer | Isocyanate | Pre-built segments, lower volatility | Elastomers, coatings, adhesives, sealants |
| Aliphatic isocyanate (HDI, IPDI) | Isocyanate | UV and colour stability | Top coats, light-stable coatings |
| Amine and metal catalysts | Additive | Reaction speed and balance | All systems |
| Silicone surfactant | Additive | Cell structure | All foams |
| Physical blowing agent | Additive | Density, insulation value | Rigid insulation foam |
| Flame retardant | Additive | Fire classification | Construction, transport |
| Chain extender (MEG, DEG, BDO) | Additive | Hardness, hard segments | Soles, elastomers, integral skin |
| Plasticizer, filler, colorant, release agent | Additive | Processing and appearance | Footwear, moulded parts, coatings |
Pluskim supplies fifteen of these products as individual raw materials, from polyether polyols and isocyanates to glycols, catalysts, silicone surfactants, glass beads and phthalic anhydride; the full list is on its raw materials and chemicals page.
07Which Raw Materials For Which Application?
Each end use pairs a particular polyol with a particular isocyanate and a matching additive package. In short:
- Rigid insulation foam (panels, spray, refrigerators, pipes): rigid polyether and aromatic polyester polyols with polymeric MDI, physical blowing agents and flame retardants.
- Flexible foam (mattresses, furniture, car seats): high molecular weight polyether polyols, often with polymer polyol, reacted with TDI or MDI and blown with water.
- Footwear (soles, insoles, slippers, safety shoes): polyester or polyether polyols with MDI prepolymers and chain extenders.
- CASE (coatings, adhesives, sealants, elastomers): prepolymers, aliphatic isocyanates for UV stability, and specialised polyols.
The raw materials by application guide maps each end use in detail, including typical densities and the trade-offs between buying raw materials and buying a ready system.
08Quality Parameters To Check On Every Delivery
Consistent raw materials make consistent parts. A short incoming inspection against the certificate of analysis (CoA) catches most problems before they reach the line.
| Parameter | Applies to | Why it matters | Common method |
|---|---|---|---|
| Hydroxyl value (mg KOH/g) | Polyols, blends | Sets the isocyanate demand; a drift changes the index and the final hardness | ASTM D4274 / titration |
| NCO content (%) | Isocyanates, prepolymers | Sets the mixing ratio; low NCO means ageing or moisture contamination | ASTM D5155 / titration |
| Viscosity (mPa·s at 25 °C) | All liquids | Affects pumping, mixing quality and machine settings | Rotational viscometer |
| Water content (%) | Polyols, blends | Water creates CO2; extra water shifts density and consumes isocyanate | Karl Fischer titration |
| Acid value (mg KOH/g) | Polyester polyols | High acid value slows the reaction and lowers hydrolysis resistance | Titration |
| Reactivity profile (cream, gel, tack-free time) | Formulated systems | Confirms the batch behaves like the approved one on the line | Cup test, Foamat |
Pluskim's R&D laboratory runs NCO-OH and FTIR analysers, viscosity-temperature analysis and Foamat reaction-profile measurement on its production; the Pluskim R&D and Simulation Centre describes the equipment.
09Storage, Handling And Safety
Most polyurethane raw materials are stable for months when stored correctly, but two rules apply everywhere: keep moisture out and stay within the data-sheet temperature range.
- Moisture: isocyanates react with water vapour, forming solid urea and CO2 that can pressurise a drum. Close containers immediately after use; blanket bulk tanks with dry air or nitrogen.
- Temperature: MDI grades may crystallise when cold and form insoluble dimer when stored hot for long periods; polyol blends can separate or change viscosity. Typical storage ranges sit around 15-30 °C, but the data sheet rules.
- Mixing before use: formulated polyol blends containing physical blowing agents or fillers should be homogenised before they are pumped.
- First in, first out: respect the shelf life on the CoA and rotate stock.
10Sustainable And Recycled Raw Materials
The polyurethane industry is replacing part of its fossil feedstock without changing the chemistry of the product. Three routes are already commercial:
- Recycled PET polyester polyols: post-consumer bottles and textile fibres are chemically recycled into aromatic polyester polyols for rigid foam. Pluskim describes its approach in PET recycled polyester polyol.
- Bio-based polyols: polyols derived from vegetable oils or other renewable sources replace part of the petrochemical content.
- Low-impact blowing agents: CFCs and HCFCs were phased out under the Montreal Protocol; today's rigid foams use hydrocarbons, water or HFOs with very low global warming potential.
Life-cycle data (eco-profiles) for MDI, TDI and polyols are published by ISOPA, which allows foam producers to calculate the footprint of their products.
11Sourcing Polyurethane Raw Materials
Raw materials reach converters through three kinds of supplier: primary producers of isocyanates and polyols, distributors and traders, and systems houses that formulate and produce ready systems as well as supplying individual components. The right partner depends on volume, in-house formulation skill and how much technical support the line needs.
When comparing offers, look beyond the price per kilogram: batch-to-batch consistency, documentation (TDS, SDS and a CoA per batch), technical support during line trials and reliable logistics usually decide the real cost. The articles how to choose a polyurethane raw material supplier and the true cost of cheap raw materials cover both questions.
As an example of the systems-house model, Pluskim in Istanbul has produced polyurethane systems since 2009 and supplies rigid, flexible, footwear and CASE systems alongside individual raw materials.
12Sources And Further Reading
- ISOPA, European Diisocyanate & Polyol Producers Association: Applications of polyurethanes
- ISOPA: REACH restriction on diisocyanates
- Official Journal of the EU: Commission Regulation (EU) 2020/1149
- ASTM International: D4274, hydroxyl numbers of polyols and D5155, isocyanate content
- American Chemistry Council: Center for the Polyurethanes Industry
- UNEP OzonAction: About the Montreal Protocol
13Frequently Asked Questions
What Are The Main Raw Materials Of Polyurethane?
Polyurethane is made from two main raw materials: a polyol (a molecule with several hydroxyl groups, usually a polyether or polyester) and an isocyanate (mainly MDI or TDI). They are combined with additives such as catalysts, silicone surfactants, blowing agents, flame retardants and chain extenders, which control reaction speed, cell structure, density and fire behaviour.
What Is The Mixing Ratio Of Polyol To Isocyanate?
There is no single ratio. It is calculated from the hydroxyl value of the polyol blend and the NCO content of the isocyanate, then adjusted by the isocyanate index. Flexible foams are usually run close to stoichiometry (index around 100-115), while PIR insulation uses a large excess of isocyanate (index often 250 or higher). The supplier's data sheet gives the recommended weight ratio for a ready system.
What Is The Difference Between The A Side And The B Side?
They are the two components of a polyurethane system, but the naming depends on the region. In North America the A side is usually the isocyanate and the B side the polyol blend (resin). In much of Europe and Türkiye, component A often means the polyol blend and component B the isocyanate. Always confirm by the chemical name on the label and SDS, never by the letter.
Is Polyurethane Made From Petroleum?
Most polyurethane raw materials are derived from petrochemicals: propylene oxide and ethylene oxide for polyether polyols, benzene and toluene for MDI and TDI. A growing share comes from alternative feedstocks, including polyester polyols made from recycled PET, bio-based polyols from vegetable oils, and mass-balance certified isocyanates. The chemistry of the final polymer is the same.
How Should Polyurethane Raw Materials Be Stored?
Keep containers tightly closed in a dry, covered area, within the temperature range on the data sheet (commonly about 15-30 °C). Isocyanates react with moisture, so drums should be closed straight after use and bulk tanks kept under dry air or nitrogen. MDI can crystallise or form dimer if stored too cold or too hot, and some polyols separate if left unmixed.
Can Polyurethane Raw Materials Be Recycled Or Bio-Based?
Yes. Aromatic polyester polyols can be produced from post-consumer PET bottles and textiles, natural-oil polyols replace part of the fossil content, and chemical recycling (glycolysis) turns polyurethane scrap back into polyols. Producers publish eco-profiles and life-cycle data for their raw materials through industry bodies such as ISOPA.
Sourcing These Raw Materials
Comparing offers for a polyol, an isocyanate or a formulated system? The supplier checklist covers the documents to request, what to test on delivery and the red flags to watch for.
