Polyurethane System Raw Materials

Isocyanates, polyols and PU systems for foam, coating and elastomer producers: specification values, safe handling and system trials.

Buyer summary

What it is: Isocyanates, polyols and formulated polyurethane systems, the reactive components of PU foams, coatings, elastomers, adhesives and binders.
Main applications: Furniture and bedding foam, automotive seating and acoustics, building and appliance insulation, cold-chain panels, floor and industrial coatings, adhesives and sealants, cast elastomers and footwear.
Critical purchasing specifications: Target product and process: foam, coating or elastomer
Certificate values with methods: hydroxyl number (ASTM D4274), isocyanate content (ASTM D5155)
Isocyanate index and system composition
Finished-product tests (for example ASTM D3574 flexible foam, ASTM D1621 rigid foam)
Handling, storage and exposure-control documentation
Qualification considerations: Qualify the whole system, because a change in one component changes the product. Isocyanates need exposure control under OSHA and local rules.
First step: Describe the foam, coating or elastomer target, your process and your handling capability.
How PAXOMER can assist: Polyurethane raw materials are qualified as a system: isocyanate, polyol blend, catalysts and process. PAXOMER can help document the foam, coating or elastomer target and the handling constraints, identify manufacturers or system houses with suitable chemistries, and coordinate sample quantities under appropriate safety documentation. Commercial discussions follow technical fit. Manufacturer identification, qualification support and pricing discussions depend on manufacturer confirmation, specifications, quantities and terms.

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Detailed technical guidance, data tables, FAQs and technical references follow below.

Hazardous chemical handling. Some components can be sensitisers or hazardous. Follow the safety data sheet and applicable occupational health and safety rules; handling and exposure controls need qualified review.

General technical information published by PAXOMER Inc. to support preliminary material evaluation. It is compiled from the sources cited on this page and has not been independently reviewed or certified by a professional engineer, laboratory or certification body. Values marked typical, illustrative or requiring confirmation are not specifications. Confirm properties, standard editions, regulatory status and suitability for your specific application with the manufacturer and, where the use is regulated or safety-related, with a qualified professional or the relevant authority.

Polyurethanes are made by reacting isocyanates (most commonly MDI and TDI families) with polyols (polyether, polyester and specialty polyols), together with chain extenders, catalysts, surfactants, blowing agents, flame retardants and other additives. The same chemistry produces flexible and rigid foams, coatings, adhesives, sealants, elastomers and binders. Producers buy either individual raw materials or formulated systems from system houses, and qualification always concerns the reacting system, not a single drum.

This page is for foam, coating, adhesive and elastomer producers, process engineers and purchasing teams evaluating polyurethane raw materials or systems. It explains the material families, the specification values used on certificates, stoichiometry and the isocyanate index, safe handling, and how to plan a system trial. It does not state that PAXOMER stocks, manufactures or has qualified any polyurethane raw material, and its tables are a framework rather than confirmed values.

A. Product identity and terminology

1. What do polyurethane raw materials do?

Isocyanates provide reactive NCO groups; polyols provide reactive OH groups and largely set flexibility or rigidity; chain extenders and crosslinkers build hard segments; catalysts balance the gelling and blowing reactions; surfactants stabilise cells in foams; blowing agents (water producing CO₂, or physical blowing agents) expand foams; additives provide flame retardancy, colour, UV stability and processing behaviour. Manufacturer literature groups isocyanate and polyol products by market, such as flexible foam, rigid foam and coatings, adhesives, sealants and elastomers (S1).

2. Which raw-material families are used?

Polyurethane raw-material families (qualitative orientation)
Family	Typical uses	Points to evaluate
Polymeric MDI	Rigid foam, insulation, binders	NCO content, functionality, viscosity
Monomeric and modified MDI	Elastomers, coatings, adhesives, flexible foam	NCO content, freezing point, storage
TDI	Flexible slabstock and moulded foam	Isomer ratio, volatility and exposure control
Aliphatic isocyanates (for example HDI, IPDI derivatives)	Light-stable coatings	NCO content, viscosity, monomer content
Polyether polyols	Foams, elastomers, sealants	Hydroxyl number, functionality, water content
Polyester polyols	Rigid foam, coatings, adhesives, elastomers	Hydroxyl and acid number, hydrolysis resistance
Formulated systems	Ready-to-use A/B systems from system houses	Mix ratio, reactivity profile, shelf life

Comparison: open-cell versus closed-cell foam. Glossary: polyol, MDI, TDI, isocyanate index.

3. Which terms appear in specifications?

NCO content, hydroxyl number (OH number), equivalent weight, functionality, acid number, water content, viscosity, isocyanate index, mix ratio, cream time, gel time, rise time, tack-free time, density, cell structure, closed-cell content, compression set, hardness. Glossary: pot life.

B. Properties and performance

4. Which certificate values matter, and how are they measured?

For polyols, hydroxyl number is determined by ASTM D4274 (S3), together with water content, acid number and viscosity. For aromatic isocyanates, isocyanate content is determined by ASTM D5155 (S4), and viscosity of crude or modified isocyanates by ASTM D4889 (S5). Certificates should state the method and value per lot so that formulations can be adjusted.

Raw-material parameters to specify

Illustrative framework only. Values and limits come from the manufacturer's specification for the exact product.

Raw-material parameters to specify
Property	Value or range	Unit	Test conditions	Test method	Grade or construction	Source	Verification status
Hydroxyl number	target and range	mg KOH/g	Per method	ASTM D4274	Polyol	S3	Manufacturer confirmation required
Isocyanate (NCO) content	target and range	% by weight	Per method	ASTM D5155	Aromatic isocyanate	S4	Manufacturer confirmation required
Viscosity	target and range	mPa·s	Temperature stated	ASTM D4889 (isocyanates) or agreed method	Isocyanate or polyol	S5	Manufacturer confirmation required
Water content	maximum	% by weight	Method stated	Agreed method	Polyol or blend	None	Manufacturer confirmation required
Acid number	maximum	mg KOH/g	Method stated	Agreed method	Polyester polyol	None	Manufacturer confirmation required
Foam density and compression	per product	kg/m³ and kPa	Specimen and conditioning stated	ASTM D3574 (flexible) or ASTM D1621 (rigid compression)	Foam	S6, S7	Manufacturer confirmation required

5. How is the isocyanate amount calculated from the index?

Equivalent weight converts certificate values into reacting equivalents. For a polyol, equivalent weight ≈ 56,100 ÷ hydroxyl number (mg KOH/g). For an isocyanate, equivalent weight ≈ 4,202 ÷ NCO content (%). The isocyanate index is 100 × (isocyanate equivalents used ÷ hydroxyl and other reactive equivalents). The example shows the arithmetic for a polyol alone; real formulations also count water, chain extenders and other reactive components.

The calculation shows why lot-to-lot changes in hydroxyl number or NCO content must be fed back into the mix ratio: a different certificate value changes the equivalents and therefore the index.

Hypothetical isocyanate-index calculation

Hypothetical example to show the arithmetic. Certificate values are illustrative; real formulations include water and other reactive components and follow the system house's guidance.

Hypothetical isocyanate-index calculation
Property	Value or range	Unit	Test conditions	Test method	Grade or construction	Source	Verification status
Polyol hydroxyl number	56	mg KOH/g	Illustrative certificate value	Input	Hypothetical polyol	None	Hypothetical calculation
Polyol equivalent weight	1001.8	g/eq	56100 / 56	Arithmetic	Hypothetical polyol	None	Hypothetical calculation
Isocyanate NCO content	31.5	%	Illustrative certificate value	Input	Hypothetical isocyanate	None	Hypothetical calculation
Isocyanate equivalent weight	133.4	g/eq	4202 / 31.5	Arithmetic	Hypothetical isocyanate	None	Hypothetical calculation
Polyol equivalents in 100 g	0.0998	eq	100 / 1001.8	Arithmetic	Hypothetical	None	Hypothetical calculation
Isocyanate needed at index 105	13.98	g per 100 g polyol	0.0998 × 1.05 × 133.4	Arithmetic	Hypothetical	None	Hypothetical calculation

6. Why do reactivity and processing profiles matter?

Cream, gel, rise and tack-free times describe how a system reacts; they depend on temperature, catalysts, water content and mixing. A change in raw-material lot, ambient temperature or catalyst level can move the profile enough to cause defects. Measure reactivity at agreed conditions during incoming checks for critical systems.

C. Manufacturing and processing

7. How are polyurethane products processed?

Components are metered and mixed by high- or low-pressure dispensing machines, then poured, sprayed, injected or cast. Flexible slabstock is made on continuous conveyors; moulded foam in heated moulds; rigid insulation on laminators or by spray; elastomers by casting; coatings and adhesives by spray, roller or bead. Temperature control of components and moulds and the accuracy of the mix ratio are critical.

8. Which production problems are common?

Problems, possible causes and first checks
Problem	Possible causes	First checks
Foam collapse or splits	Catalyst balance, surfactant, temperature, index	Reactivity profile; component temperatures; index
Coarse or irregular cells	Mixing, surfactant, contamination	Mix head condition; surfactant level
Soft or tacky product	Low index, off-ratio mixing, moisture	Mix ratio calibration; certificate values
Brittle or friable rigid foam	High index, low temperature, formulation	Index; component and mould temperatures
Shrinkage after demould	Closed cells, cure, density	Cell opening; cure time
Bubbles in elastomers or coatings	Moisture, inadequate degassing	Water content; degassing step

9. How should isocyanates and polyols be handled safely?

Isocyanates can cause respiratory and skin sensitisation. OSHA provides an overview of isocyanate hazards, exposure controls and protective measures (S2). Follow the safety data sheet, provide ventilation and exposure monitoring as required, use appropriate respiratory and skin protection, and train workers. In Canada, workplace chemical hazard communication follows WHMIS and provincial occupational health and safety rules apply.

10. How should raw materials be stored?

Keep isocyanates dry: moisture reacts with NCO groups, forming CO₂ and solids, which can pressurise containers. Store within the manufacturer's temperature range; some MDI types crystallise or freeze when cold and need controlled warming. Keep polyols dry and mixed if they contain dispersed components. Observe shelf life and nitrogen blanketing guidance for bulk storage.

D. Applications and qualification

11. Where are polyurethane systems used?

Furniture and bedding foam, automotive seating and acoustic parts, building insulation and spray foam, appliance insulation, cold-chain panels, coatings for floors and industrial surfaces, adhesives and sealants, cast elastomers for wheels and rollers, footwear, and composite binders.

12. Which requirements depend on the application?

Building insulation must meet product and code requirements for thermal and fire performance; furniture foam may need flammability documentation; automotive parts follow OEM specifications and emissions limits; coatings may need VOC limits; food-contact or medical uses need specific documentation. Define these before selecting raw materials.

13. How should a producer select raw materials or a system?

Describe the product, process, equipment and performance targets.
Decide whether to buy individual raw materials or a formulated system.
Ask manufacturers for specifications, typical values with methods and processing recommendations.
Run laboratory reactivity and property tests, then machine trials.
Agree certificate values, acceptance limits and change notification before production.

14. How should a system trial be run?

Condition components to the process temperature, calibrate the mix ratio, record reactivity times, and make parts at the target index and slightly above and below it to understand sensitivity. Test product properties against the incumbent. Record lot numbers and certificate values for every component.

15. Which documents should be requested?

Product specification and lot certificates with methods; technical data sheet; safety data sheet; handling and storage guidance; processing recommendations; regulatory statements for the application; and change-notification commitment covering raw-material and site changes.

E. Procurement, comparisons and decisions

16. How do polyurethanes compare with alternative chemistries?

Alternatives compared (qualitative)
Alternative	Where it may be preferred	Trade-offs to evaluate
Polyurethane	Versatile foams, elastomers, coatings and adhesives	Isocyanate handling, moisture sensitivity
Epoxy systems	Rigid coatings and adhesives, chemical resistance	Brittleness, cure temperature; see epoxy and coating resin systems
Silyl-modified polymers	Isocyanate-free sealants and adhesives	Mechanical properties by grade; see sealants
Polyolefin and other thermoplastic foams	Recyclable foams, chemical resistance	Different processing; see foam sheets and rolls

17. What determines total cost?

Raw-material prices, density and yield, scrap, cycle time, energy for heating components and moulds, safety and ventilation costs, and the cost of defects. A system with a wider processing window can reduce scrap and total cost.

18. What should a polyurethane raw-material RFQ include?

Product, process, equipment and target properties.
Raw materials or system required, with specification values and methods.
Regulatory, fire, emissions or VOC requirements.
Packaging (drums, IBCs, bulk), storage capability and safety arrangements.
Annual volume, delivery location and schedule.

Prepare and submit these through the RFQ brief.

19. Which manufacturer qualification questions should be asked?

Product range and system-house capability; certificate methods; technical support for trials; product stewardship and safety training; logistics for hazardous goods; regional supply; and change control. PAXOMER does not confirm any manufacturer's capabilities on this page.

Guide: Polyurethane raw materials
Related page: Polyiso insulation boards and facers
Related page: Industrial foam sheets and rolls
Related page: Solvent-free laminating adhesives

Manufacturing Regions & International Supply

Countries where public company or trade sources document manufacturing relevant to Polyurethane System Raw Materials, with the form of material made there and the date of the evidence. A listing is market context only. It does not indicate a PAXOMER relationship, availability or price.

South Korea: MDI production in Yeosu, with an expansion due in 2027. Product manufacturing · Trade report, 2025–2026 · R37
China: MDI production at an integrated site in Shanghai, where a further MDI train is planned. Product manufacturing · Trade report, 2026 · R36

If you are evaluating manufacturers abroad, list in your RFQ brief the destination market, the documents you require and the delivery terms.

Engineering and purchasing FAQs

Each answer is general technical information, not a specification or a quotation.

What is the isocyanate index?

It is 100 times the ratio of isocyanate equivalents used to the stoichiometric amount needed for all reactive groups. An index of 105 means 5 % more isocyanate than stoichiometric.

Why must certificate values feed into the mix ratio?

Hydroxyl number and NCO content vary within specification from lot to lot. They change the equivalents, so the mix ratio may need adjustment to keep the index constant.

Should I buy a formulated system or individual raw materials?

Systems simplify formulation and support; individual materials give more control and may reduce cost at scale but require formulation capability. The choice depends on volume, expertise and equipment.

Why does MDI need careful storage?

Moisture reacts with isocyanate, forming CO₂ and solids, and some types crystallise or freeze when cold. Keep containers dry and within the stated temperature range.

What safety measures apply to isocyanates?

Exposure control through ventilation, monitoring, respiratory and skin protection, and training, following the safety data sheet and applicable occupational health and safety rules.

Can PAXOMER help source polyurethane raw materials?

This page does not confirm supply. Send your product, process and specification requirements, and PAXOMER will review whether a suitable manufacturer-development opportunity exists.

Technical References

References below were opened on the access date shown. A source supports only the statement it is cited for. Standards are cited by number and title from public catalogue entries; their full text was not read unless stated.

S1. Isocyanate and Polyol Products. BASF. chemicals.basf.com/north-america/en/Monomers/isocyanates-and-polyols/products (opens in a new tab) manufacturer literature · accessed 2026-10-28
Product overview opened 2026-10-28; cited for the grouping of isocyanate and polyol products by market. Not an endorsement.
S2. Isocyanates — Overview. US Occupational Safety and Health Administration (OSHA). www.osha.gov/isocyanates (opens in a new tab) regulatory · accessed 2026-10-28
Topic page opened 2026-10-28; cited for the existence of US guidance on isocyanate hazards and controls.
S3. ASTM D4274: Standard Test Methods for Testing Polyurethane Raw Materials: Determination of Hydroxyl Numbers of Polyols. ASTM International. store.astm.org/standards/d4274 (opens in a new tab) standard catalogue · accessed 2026-10-28
Catalogue entry opened 2026-10-28 to confirm number and title; full text not read.
S4. ASTM D5155: Standard Test Methods for Polyurethane Raw Materials: Determination of the Isocyanate Content of Aromatic Isocyanates. ASTM International. store.astm.org/standards/d5155 (opens in a new tab) standard catalogue · accessed 2026-10-28
Catalogue entry opened 2026-10-28 to confirm number and title; full text not read.
S5. ASTM D4889: Standard Test Methods for Polyurethane Raw Materials: Determination of Viscosity of Crude or Modified Isocyanates. ASTM International. store.astm.org/standards/d4889 (opens in a new tab) standard catalogue · accessed 2026-10-28
Catalogue entry opened 2026-10-28 to confirm number and title; full text not read.
S6. ASTM D3574: Standard Test Methods for Flexible Cellular Materials—Slab, Bonded, and Molded Polyurethane Foams. ASTM International. store.astm.org/standards/d3574 (opens in a new tab) standard catalogue · accessed 2026-10-28
Catalogue entry opened 2026-10-28 to confirm number and title; full text not read.
S7. ASTM D1621: Standard Test Method for Compressive Properties of Rigid Cellular Plastics. ASTM International. store.astm.org/standards/d1621 (opens in a new tab) standard catalogue · accessed 2026-10-28
Catalogue entry opened 2026-10-28 to confirm number and title; full text not read.
S8. Polyurethane raw materials (PAXOMER guide). PAXOMER Inc., 2026-10-28. /products/polyurethane-raw-materials/ technical literature · accessed 2026-10-28
PAXOMER’s own guide; not an external source and not independently reviewed.

Regional manufacturing evidence

Company and trade publications cited in Manufacturing Regions & International Supply. Each supports only the statement it is cited for (checked 29–30 October 2026). Naming a company here does not state or imply a relationship with PAXOMER.

R36. Covestro announces investment program for MDI (Shanghai integrated site). CHEManager International. chemanager-online.com/en/news/covestro-announces-investment-program-for-mdi (opens in a new tab) checked 2026-10-30
R37. Kumho Mitsui JV to increase MDI production capacity (Yeosu). European Rubber Journal. www.european-rubber-journal.com/article/2098553/kumho-mitsui-jv-to-increase-mdi- (opens in a new tab) checked 2026-10-30

Evidence notes and limitations

What the information on this page does not establish. Confirm these points with the manufacturer, the current standard or the relevant authority before relying on them.

Standards are cited by number and title; scopes and editions were not read.
The equivalent-weight constants (56,100 and 4,202) are standard textbook relations and are not supported by a recorded source on this page.
Raw-material family descriptions are general practice and not supported line by line by a recorded source.
Canadian WHMIS and provincial OHS rules are mentioned generically; the Health Canada pages could not be opened on 2026-10-28.
This page has not been independently technically reviewed or certified.

Facts checked against the cited sources

Titles of ASTM D4274, D5155, D4889, D3574 and D1621 were confirmed on the ASTM catalogue on 2026-10-28.
The BASF isocyanate and polyol overview and the OSHA isocyanates page were confirmed to exist on 2026-10-28.
The index arithmetic (56100/56 = 1001.8; 4202/31.5 = 133.4; 0.0998 × 1.05 × 133.4 = 13.98 g) was checked.

Where this connects to the full guide

The primary technical guide behind this page is Polyurethane Raw Materials: MDI, TDI, Polyols & PU Systems. All its topics are indexed below.

Topics in the full guide

See all 33 topics in the guide

Glossary: Methylene diphenyl diisocyanate · Toluene diisocyanate · Polyol · Isocyanate index · Prepolymer

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