The cost of polyurethane raw materials is usually discussed as a price per kilogram, because that is the number on every quotation. A plant, however, does not sell kilograms of polyol. It sells panels, mattresses, seats or pairs of soles, and the raw material that is cheapest per kilogram is not always the cheapest per finished unit. This article sets out a simple model for making that comparison properly.
The real cost of a polyurethane raw material is its cost per good finished unit: kilograms used per part at the density needed to meet specification, times price per kilogram, plus conversion cost per shot, divided by the yield of good parts, plus quality costs. A 10 % lower price per kilogram can easily become a higher cost per part.
- Compare offers per good part, per square metre of panel or per pair of soles, not per kilogram.
- Density, scrap and cycle time are the three levers that most often cancel a price saving.
- Quality costs come later: claims, rework and failed fire tests appear months after the purchase decision.
- Trials must be long enough to show batch-to-batch consistency, not just a good first shot.
- Write consistency into the contract: specification ranges, a certificate of analysis per batch and change notification.
01Price Per Kilogram Versus Cost Per Unit
Price per kilogram measures what a raw material costs to buy; cost per unit measures what it costs to turn into saleable product. The second figure is the one that reaches the profit and loss account.
The gap between the two exists because polyurethane is a reactive system. Small differences in a polyol's hydroxyl value, functionality, water content or reactivity, or in an isocyanate's NCO content, change how the foam rises, cures and performs. The plant then compensates, usually by adding material, slowing the line or accepting more rejects. Each of those adjustments has a cost that never appears on the quotation.
The useful unit depends on the product:
- Moulded parts (seats, soles, integral skin): cost per good part.
- Continuous panels: cost per square metre at the required thickness and thermal performance.
- Slabstock foam: cost per cubic metre of saleable block after trimming.
- Footwear: cost per pair of soles that pass inspection.
02A Simple Total Cost Model
A workable model needs only four inputs that every plant already tracks: material use per unit, price, conversion cost and yield. Quality costs are added on top.
Cost per good unit = (kg per unit × price per kg + conversion cost per unit) ÷ (1 − scrap rate) + quality costs per unit
- kg per unit is set by the density needed to meet the hardness, strength or insulation specification, not by the density the supplier quotes.
- Conversion cost covers labour, energy, machine depreciation and mould time. It is charged per shot, per minute of mould occupancy or per metre of line.
- Scrap rate is the share of output that fails inspection. Every rejected unit carries its full material and conversion cost.
- Quality costs include rework, extra additives, customer claims, returns and repeated certification tests.
03Worked Example: Two Polyol Offers
The example below compares two offers for the same moulded flexible foam part with a volume of 10 litres. Offer B is 10 % cheaper per kilogram. All figures are illustrative figures, not market prices: round numbers chosen to show how the model works.
| Item | Offer A | Offer B |
|---|---|---|
| System price per kg | 3.00 | 2.70 |
| Density needed to meet hardness spec | 55 kg/m³ | 60 kg/m³ |
| Material per part (10 L) | 0.55 kg | 0.60 kg |
| Demould time per shot | 4 min | 5 min |
| Scrap rate | 2 % | 6 % |
| Material cost, 100 shots | 165.00 | 162.00 |
| Conversion cost, 100 shots (0.30 per mould-minute) | 120.00 | 150.00 |
| Total cost, 100 shots | 285.00 | 312.00 |
| Good parts | 98 | 94 |
| Cost per good part | 2.91 | 3.32 |
Offer B saves 3.00 in material over 100 shots but costs 27.00 more in total, so each good part is about 14 % more expensive. The calculation is conservative: it ignores claims, extra cleaning and any additional catalyst needed to rescue the reaction profile.
The same numbers show how large the price gap would have to be. For Offer B to match Offer A's cost per good part at 60 kg/m³, 5-minute demould and 6 % scrap, it would need to be priced at about 2.06 per kilogram, roughly 31 % below Offer A rather than 10 %. That break-even figure is often the most persuasive number to bring into a purchasing meeting.
04The Hidden Cost Drivers
Most of the extra cost of a poorly matched raw material comes from a short list of mechanisms. Each can be measured, which is what makes the model practical.
Density Creep
If the foam is softer or weaker than expected, density goes up until the part passes. A few kilograms per cubic metre across a year's output is a significant tonnage.
Scrap And Off-Spec Batches
Voids, shrinkage, splits, poor skin or dimensional faults send parts to the bin. Off-spec batches of raw material can stop a line entirely while the cause is found.
Line Speed And Demould Time
A slower cure means fewer shots per mould per shift, or a slower conveyor on a continuous line. Capacity lost this way is often more expensive than the raw material itself.
Extra Additives
Inconsistent reactivity is frequently corrected with more catalyst, surfactant or blowing agent. The correction adds cost and makes the formulation more sensitive to the next variation. The additives guide explains what each of these components does.
Cleaning, Filters And Downtime
Sediment, high water content or incompatible components foul filters, mixheads and dosing pumps. Unplanned maintenance carries labour, spare parts and lost production.
Failed Certification Tests
For insulation panels and spray foam, a failed fire or thermal performance test means repeating the test and, in the worst case, a delayed project or a lost approval.
Claims And Returns
Premature ageing, shrinkage or loss of resilience shows up in the field, often long after the raw material invoice has been paid. The cost includes replacement, logistics and the customer's confidence.
Storage Losses
Moisture pick-up, crystallisation or a short shelf life can make part of a delivery unusable. Correct storage, as described in ISOPA's logistics guidelines, matters as much as the purchase price.
Pluskim's own articles take a closer look at the hidden costs in polyurethane systems and at why cheap raw materials raise total cost, with examples from production.
05What To Measure In A Trial
A trial should produce the inputs for the cost model, not just a yes or no. Run it long enough to cover several raw material batches and normal shift-to-shift variation.
| Measure | How | Cost lever it reveals |
|---|---|---|
| Overall and core density | Weigh parts or cut samples | kg per unit |
| Hardness or compressive strength | Indentation hardness, Shore, compression test | Whether density had to rise to pass |
| Reaction profile | Cream, gel and tack-free times; rise profile | Consistency between batches, additive corrections |
| Demould or cure time | Time to safe demould without deformation | Conversion cost per unit |
| Scrap rate | Rejects per shift, by defect type | Yield |
| Dimensional stability | Measure after conditioning | Later claims and returns |
| Thermal conductivity, fire behaviour | Lambda measurement, relevant fire test | Certification risk for insulation |
Incoming quality control supports the trial. Hydroxyl number and NCO content are measured by standard methods (for example ASTM D4274 and ASTM D5155), and comparing these results with the supplier's certificate of analysis shows whether the documentation can be trusted.
A supplier with its own application facilities can shorten this work. Pluskim's R&D and Application and Simulation Centre runs formulations on a high-pressure dispensing system that reproduces series production conditions, together with reaction profile measurement and NCO-OH and FTIR analysis, before a system goes onto a customer's line.
06How To Negotiate On Value
Once cost per good unit is known, the negotiation can move from price alone to the conditions that keep that cost stable.
- Specification ranges in the contract for the parameters that drive your process: OH value, viscosity, water content, acid value, NCO content and reactivity.
- A certificate of analysis with every batch, plus retained samples so that disputes can be settled with data.
- Change notification: advance notice before any change in formulation, raw material source or production site.
- Technical support with a defined response time, so that a problem on the line is handled in hours rather than weeks.
- Delivery and storage terms that suit your consumption, so material does not age in the warehouse.
A checklist for comparing suppliers on these points is in our guide on how to choose a polyurethane raw material supplier, and the main raw material groups are summarised in the polyurethane raw materials guide.
07Sources And Further Reading
- ASTM D4274, standard test methods for hydroxyl numbers of polyols: store.astm.org/d4274-21.html
- ASTM D5155, standard test methods for isocyanate content of aromatic isocyanates: store.astm.org/d5155-19.html
- ISOPA, logistics guidelines for diisocyanates and polyols: isopa.org/logistics
- ISOPA, product information: isopa.org/product-information
08Frequently Asked Questions
How Do You Calculate The Real Cost Of A Polyurethane Raw Material?
Convert the offer to cost per good finished unit: kilograms used per part (at the density needed to meet the specification) multiplied by price per kilogram, plus the conversion cost of each shot or metre of line, all divided by the share of output that passes inspection. Then add quality costs such as rework, claims and extra additives. Compare suppliers on that figure, not on price per kilogram.
Why Can A Cheaper Polyol Increase Density?
If a polyol has a different molecular weight, functionality or reactivity than the one the formulation was built on, the foam may come out softer or weaker at the same density. To bring hardness or compressive strength back into specification, the plant raises density, which means more kilograms per part. A small saving per kilogram can disappear once more material goes into every unit.
What Should Be Measured In A Raw Material Trial?
Measure the properties that drive cost and quality over a realistic run: overall and core density, hardness or compressive strength, reaction profile (cream, gel and tack-free times), demould or cure time, line speed, scrap rate per shift, dimensional stability and, for insulation, thermal conductivity and fire test results. Use several batches, not one, so that batch-to-batch consistency is visible.
Is The Cheapest Raw Material Ever The Right Choice?
Yes, when the trial shows equal density, equal scrap rate, equal cycle time and consistent batches. Then the lower price is a genuine saving. The point of a cost-per-good-part model is not to reject low prices but to check whether they survive contact with the production line before a contract is signed.
What Should A Raw Material Contract Include Besides Price?
Agreed specification ranges for the parameters that matter (for example OH value, viscosity, water content, NCO content and reactivity), a certificate of analysis with every batch, retained samples, advance notice of any change in formulation or source, delivery lead times, and access to technical support when a problem appears on the line. These clauses protect the cost model the purchase was based on.
09Related Reading
- How To Choose A Polyurethane Raw Material Supplier: A 2026 ChecklistA 2026 buyer's checklist for choosing a polyurethane raw material supplier: documents, batch checks, technical support, logistics and red flags to avoid.
- Polyurethane Raw MaterialsPolyurethane raw materials explained: polyols, MDI and TDI, prepolymers and additives, with typical specs, a full material list and sourcing advice.
- Polyols For PolyurethanePolyols for polyurethane explained: polyether, polyester, polymer and bio-based grades, OH value, functionality and how to choose one per application.
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.