Choosing polyurethane raw materials by application starts with the end product: an insulation panel needs closed cells and fire performance, a mattress needs open cells and resilience, a shoe sole needs abrasion resistance and a coating needs adhesion and UV stability. This guide maps each major application to the polyol, isocyanate and additive families it normally uses, and explains when a ready-to-use system makes more sense than buying raw materials separately.
Rigid foam uses high-functionality polyether or aromatic polyester polyols with polymeric MDI and physical blowing agents. Flexible foam uses long-chain polyether triols with TDI or MDI and water. Footwear uses polyester or polyether polyols with MDI prepolymers. Coatings, adhesives, sealants and elastomers (CASE) use prepolymers, and aliphatic isocyanates where UV stability is required.
- Polyol functionality and molecular weight decide whether a polyurethane ends up rigid or flexible.
- Polymeric MDI dominates rigid foam; TDI 80/20 dominates flexible slabstock; MDI prepolymers dominate footwear, binders and many adhesives.
- Aliphatic isocyanates are chosen only where colour and gloss must survive sunlight, because they cost more than aromatic ones.
- Additive packages differ completely between applications, even when the base polyol is similar.
- Most processors buy formulated systems; integrated producers often buy individual raw materials.
01Raw Materials By Application At A Glance
The table summarises the typical raw material choice for each major application. Values are general industry ranges for orientation, not product specifications.
| Application | Polyol type | Isocyanate | Key additives | Typical density or property |
|---|---|---|---|---|
| Continuous sandwich panels | Polyether and aromatic polyester polyol blends | Polymeric MDI (high index for PIR) | Pentane or HFO, water, amine and potassium catalysts, TCPP, silicone | 38-45 kg/m³ core |
| PIR insulation boards | Aromatic polyester polyols | Polymeric MDI, index often above 250 | Pentane, trimer catalysts, flame retardant, silicone | 30-35 kg/m³ |
| Closed-cell spray foam | Mannich, polyester and polyether polyol blends | Polymeric MDI | HFO and water, flame retardant, fast amine catalysts | 30-50 kg/m³ |
| Open-cell spray foam | Polyether polyols | Polymeric MDI | Water only, cell-opening surfactant, flame retardant | 7-12 kg/m³ |
| Refrigerators and freezers | Sucrose, sorbitol and amine-initiated polyethers | Polymeric MDI | Cyclopentane, water, flow-optimised catalysts | 30-36 kg/m³ in place |
| Pre-insulated pipes | Polyether polyol blends | Polymeric MDI | Cyclopentane or water, catalysts, silicone | 50-80 kg/m³ |
| Flexible slabstock foam | Polyether triol, about 3,000 MW; polymer polyol for firmness | TDI 80/20 | Water, tin and amine catalysts, silicone | 15-40 kg/m³ |
| HR moulded foam (seats) | Glycerine-initiated, EO-tipped high-reactivity polyether; polymer polyol | MDI or TDI/MDI blends | Water, DEOA crosslinker, amine catalysts, weak silicone | 40-65 kg/m³ |
| Viscoelastic (memory) foam | Special low-resilience polyether blends | TDI or MDI | Water, catalysts, cell openers | Slow recovery, 40-80 kg/m³ |
| Shoe soles | Polyester (adipate) or polyether polyols | MDI prepolymer | MEG chain extender, water, amine catalyst, colour paste | 0.45-0.65 g/cm³ |
| Integral skin foam | Polyether polyols | Modified MDI | Chain extender, physical blowing agent or water, release agent | Dense skin, cellular core |
| Wood imitation parts | Rigid polyether polyols | Polymeric MDI | Water, catalysts, release agent | High-density rigid foam |
| Waterproofing membranes | Polyether polyols | MDI prepolymer (aromatic) | Plasticizer, fillers, moisture scavenger | High elongation |
| UV-stable top coats | Polyester, acrylic or polyether polyols | Aliphatic (HDI, IPDI derivatives) | Tin-free or tin catalysts, UV stabilisers | Colour and gloss retention |
| Adhesives and binders | Polyether polyols | MDI prepolymer (1K moisture curing) or 2K | Catalysts, fillers | Bond strength, open time |
02Rigid Foam: Insulation And Structural Parts
Rigid polyurethane and polyisocyanurate foams are made from short-chain, highly branched polyols and polymeric MDI, producing a dense crosslinked network with mostly closed cells. The trapped blowing gas gives rigid foam one of the lowest thermal conductivities of any commercial insulation material.
Sandwich And Continuous Panels
Continuous panel lines and discontinuous (press) lines inject foam between two metal facings. Polyols are blends of polyether and aromatic polyester polyols, with pentane isomers or HFOs as blowing agent. For PIR panels, potassium catalysts promote isocyanurate formation at a high isocyanate index, improving fire behaviour. Flow, adhesion to the facing and a uniform density across the panel width are the main formulation targets.
Spray Foam
Spray foam is mixed at the gun and applied directly to walls, roofs and tanks. Closed-cell spray foam uses Mannich and polyester polyols with fast catalysts so it builds thickness on vertical surfaces; open-cell spray foam is water blown at very low density and is used for acoustic and air-sealing applications indoors.
Appliances And Pipe Insulation
Refrigerator and freezer cabinets are filled with foam that must flow through long, narrow cavities before it gels, so formulations use delayed-action catalysts and cyclopentane. Pre-insulated district heating pipes need foam that stays stable at elevated service temperatures. Pluskim's construction and insulation systems cover panels, spray and pipe insulation.
03Flexible Foam: Furniture, Bedding And Seating
Flexible foam uses long-chain polyether triols with low OH values, producing a lightly crosslinked network with open cells that recovers after compression. Water is normally the main blowing agent.
- Slabstock (block) foam is poured continuously into large blocks and cut for mattresses and upholstery. The classic formulation is a polyether triol of about 3,000 molecular weight with TDI 80/20, water, stannous octoate and an amine catalyst. Polymer polyols (SAN-filled) raise load-bearing for firmer grades.
- HR moulded foam uses highly reactive, glycerine-initiated, EO-tipped polyethers and polymer polyols, usually with MDI or a TDI/MDI blend, for car seats and premium furniture. It is cured in heated moulds and needs fast demould.
- Viscoelastic foam recovers slowly after compression and is used in pillows and mattresses. It relies on special polyether blends with a glass transition close to room temperature.
- Rebonded foam is made by binding shredded foam scrap with an MDI- or TDI-based prepolymer binder, a recycling route for slabstock trim.
The polyols guide explains how molecular weight and functionality separate flexible from rigid polyols. For furniture and bedding producers, Pluskim's furniture and foam systems include slabstock, viscoelastic, HR moulded and rebonded foam binders.
04Footwear: Soles, Insoles And Slippers
Polyurethane shoe soles are microcellular elastomers made by reacting a polyol blend with an MDI-based prepolymer in a mould. Density, hardness (usually measured in Shore A) and abrasion resistance are tuned through the polyol type, chain extender level and blowing level.
- Polyester polyol systems, typically adipate-based, give high abrasion, tear and oil resistance and are common in fashion and safety footwear.
- Polyether polyol systems resist hydrolysis and microbial attack better and stay flexible at low temperature.
- Insoles and slippers use soft, lightweight formulations where comfort and low density matter more than abrasion.
- Safety footwear adds requirements such as slip resistance, antistatic behaviour and resistance to fuels and oils; dual-density soles combine a hard outsole with a soft midsole.
Prepolymers dominate this segment because they reduce the free monomer content and make the mixing ratio easier to run on rotary moulding machines. See the isocyanates and prepolymers guide for NCO content and prepolymer types. Pluskim's footwear systems cover soles, slippers, insoles and safety footwear.
05CASE: Coatings, Adhesives, Sealants And Elastomers
CASE applications use polyurethane chemistry without foaming, or with only minimal gas. Prepolymers and moisture curing are common because they allow one-component products that cure in the air.
Coatings And Waterproofing
Liquid-applied waterproofing membranes are often aromatic, MDI prepolymer-based systems that cure with atmospheric moisture or as two-component products. Because aromatic polyurethanes yellow and chalk in sunlight, exposed surfaces receive a top coat based on aliphatic isocyanates such as HDI or IPDI derivatives. Polyurea, formed from isocyanates and amine-terminated resins, cures in seconds and is spray-applied for heavy-duty protection.
Adhesives And Sealants
One-component adhesives and sealants are MDI prepolymers that cure with moisture; two-component adhesives mix a polyol and an isocyanate for faster, controlled cure. Sandwich panel adhesives, wood adhesives and flooring adhesives each balance open time, green strength and final bond strength differently.
Cast Elastomers
Cast elastomers for rollers, wheels and industrial parts are made from MDI or TDI prepolymers cured with diols such as 1,4-butanediol or with aromatic diamines. They combine high load-bearing with abrasion and tear resistance.
For safety reasons, CASE products containing monomeric diisocyanates fall under the EU REACH training requirement described by ISOPA. Pluskim's coatings and waterproofing range includes PU and polyurea systems, primers and top coats.
06Binders: Sports Surfaces, Stone And Recycled Foam
Polyurethane binders glue granules or fibres together into a solid, elastic layer. They are usually one-component MDI-based prepolymers that cure with moisture.
- EPDM and tartan binders bind rubber granules into running tracks, playgrounds and sports floors.
- Stone and marble binders fix decorative aggregates for permeable paving and decorative floors; aliphatic grades are used where colour stability matters.
- Rebonded foam binders turn flexible foam scrap into new blocks for carpet underlay and mats.
07Integral Skin And Wood Imitation
Integral skin foam forms a dense outer skin and a cellular core in a single moulding step, because the foam densifies against the cooler mould wall. It is used for steering wheels, armrests and furniture parts, typically with polyether polyols, modified MDI and a chain extender.
Wood imitation systems are high-density rigid foams moulded with a surface texture that reproduces carved wood. They are used for decorative profiles, frames and furniture components where carved timber would be costly or unstable.
08Matching Raw Materials To Performance Targets
Whatever the application, the raw material choice follows from a short list of measurable targets. Writing them down before talking to a supplier saves trial rounds and makes quotations comparable.
- Density and hardness: set mainly by blowing level, polyol molecular weight and chain extender or crosslinker content.
- Thermal conductivity: set by closed-cell content, cell size and the blowing gas, so surfactant and blowing agent matter most.
- Fire class: set by isocyanate index, polyol type (aromatic polyester polyols help) and flame retardant level.
- Process window: cream time, gel time and demould time, set by the catalyst package and component temperatures.
- Durability: hydrolysis, UV, oil and abrasion resistance, set by the choice between polyester and polyether polyols and between aromatic and aliphatic isocyanates.
The additives guide covers the levers for the process window and fire class in detail.
09Raw Materials Or A Formulated System?
Polyurethane is supplied in two ways: as individual raw materials (polyols, isocyanates and additives bought separately) or as a formulated system, where a systems house delivers a ready polyol blend (the A component) and the matching isocyanate (the B component) at a fixed mixing ratio.
| Factor | Individual raw materials | Formulated system |
|---|---|---|
| In-house expertise needed | Formulation chemists and a laboratory | Process operators; supplier provides formulation |
| Recipe control | Full control, proprietary recipes | Supplier's formulation, tuned to your line |
| Material cost per kg | Usually lower | Includes formulation and support |
| Inventory | Many tanks and drums to manage | Two components |
| Troubleshooting | Your responsibility | Shared with the systems house |
| Best suited to | Large, integrated producers | Most processors and new product lines |
Buying individual raw materials makes sense when volumes are high, the recipe is stable and there is a team to qualify every new lot. A formulated system makes sense when the priority is a working product on the line quickly, a fire or density target must be met, or the product range is wide and changes often. A systems house such as Pluskim develops and supplies both: formulated systems for specific applications and individual raw materials for producers who blend their own. The supplier selection checklist covers what to ask in either case, and the main polyurethane raw materials guide explains each component in detail.
10Sources And Further Reading
- ISOPA, polyurethane applications: isopa.org
- ISOPA, REACH restriction on diisocyanates: isopa.org
- PU Europe, polyurethane insulation: pu-europe.eu
- ALIPA, aliphatic isocyanates: alipa.org
- American Chemistry Council, Center for the Polyurethanes Industry: americanchemistry.com
11Frequently Asked Questions
Which Raw Materials Are Used For Rigid Polyurethane Foam?
Rigid foam typically combines high-functionality, high-OH-value polyols (sucrose, sorbitol, Mannich or amine-initiated polyethers, often blended with aromatic polyester polyols) with polymeric MDI. Water plus a physical blowing agent such as cyclopentane, pentane or an HFO creates the closed cells, and catalysts, silicone surfactants and flame retardants complete the formulation.
Which Raw Materials Are Used For Flexible Polyurethane Foam?
Flexible slabstock foam is usually made from a polyether triol of around 3,000 molecular weight, TDI 80/20, water as the blowing agent, an amine and tin catalyst package and a silicone surfactant. HR moulded and viscoelastic foams use more specialised polyethers, polymer polyols and MDI or TDI/MDI blends.
What Raw Materials Are Used For Polyurethane Shoe Soles?
Most polyurethane shoe soles are microcellular elastomers made from a polyester polyol (often adipate-based) or a polyether polyol, an MDI-based prepolymer, a short-chain glycol such as monoethylene glycol as chain extender, water as blowing agent, catalysts, surfactant and colour paste. Polyester systems give high abrasion and oil resistance; polyether systems give better hydrolysis resistance.
What Is A Polyurethane System?
A polyurethane system is a ready-to-use two-component product. One component is a fully formulated polyol blend containing catalysts, surfactants, blowing agents and other additives; the other is the isocyanate or an isocyanate prepolymer. The processor only meters and mixes the two at a set ratio, instead of sourcing and blending individual raw materials.
Why Are Aliphatic Isocyanates Used In Coatings?
Aromatic isocyanates such as MDI and TDI yellow and chalk when exposed to sunlight. Aliphatic isocyanates such as HDI and IPDI derivatives keep their colour and gloss under UV, so they are used for top coats, floor finishes and exterior coatings. Aromatic systems remain common for waterproofing membranes and primers that are later protected by an aliphatic top coat.
Should I Buy Polyurethane Raw Materials Or A Formulated System?
Large producers with their own formulation chemists and laboratory often buy individual raw materials to control cost and recipes. Most processors buy a formulated system from a systems house because it arrives tuned to their machine, density and fire class, with technical support included. Many companies combine both approaches for different product lines.
12Related Reading
- Polyols For PolyurethanePolyols for polyurethane explained: polyether, polyester, polymer and bio-based grades, OH value, functionality and how to choose one per application.
- Isocyanates For Polyurethane: MDI, TDI And PrepolymersIsocyanates for polyurethane: MDI, polymeric MDI, TDI, aliphatics and prepolymers, NCO content, isocyanate index, safe storage and EU training rules.
- Polyurethane AdditivesPolyurethane additives explained: catalysts, silicone surfactants, blowing agents, flame retardants and chain extenders, with typical dosages and fixes.
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.