Polyether polyol is the backbone of flexible polyurethane foam — it typically makes up 60–70% of your formulation by weight. Choose the wrong grade, and you'll get foam that's too hard, too soft, collapses during rise, or fails your customer's specifications. This guide explains the three critical parameters every formulator and purchasing manager needs to understand: OH value, molecular weight, and functionality.
1. What Is Polyether Polyol and Why Does It Matter?
Polyether polyols are produced by polymerizing propylene oxide (PO) and ethylene oxide (EO) onto a starter molecule (typically glycerol). The resulting polyol is a liquid with reactive hydroxyl (-OH) groups at the ends of the polymer chains. When mixed with isocyanate (TDI or MDI), these OH groups react to form urethane linkages — creating the polyurethane polymer network.
In flexible foam, the polyol choice determines:
- Foam softness vs firmness (load-bearing capacity)
- Resilience (bounce-back)
- Cell structure (open vs closed cells)
- Processing behavior (cream time, rise time, cure)
- Long-term durability (fatigue resistance, hydrolysis stability)
2. Three Critical Parameters for Polyol Selection
2.1 OH Value (Hydroxyl Number) — The Master Control
OH value is measured in mg KOH/g and represents the concentration of reactive hydroxyl groups in the polyol — it's the single most important specification.
| OH Value Range | Typical MW | Foam Type | Feel |
|---|---|---|---|
| 50–60 mg KOH/g | 3000–3500 | Conventional flexible foam | Soft, low density |
| 28–35 mg KOH/g | 4800–6000 | High resilience (HR) foam | Firm but springy |
| 160–180 mg KOH/g | 700–800 | Memory foam (viscoelastic) | Slow recovery, "dead" feel |
Rule of thumb: Lower OH value = longer polymer chains = softer, more elastic foam. Higher OH value = shorter chains = firmer, more crosslinked foam.
How to use OH value in your spec sheet:
- Verify the OH value on every Certificate of Analysis (COA)
- Acceptable tolerance: ±2 mg KOH/g for conventional polyols, ±1.5 for HR grades
- A drift in OH value by even 3 points can measurably change foam hardness
2.2 Molecular Weight (MW) — Chain Length
Molecular weight is directly related to OH value (they're inversely proportional for a given functionality):
- MW 2000 (OH ~56): Workhorse grade for conventional furniture foam — good balance of processability and physical properties
- MW 3000 (OH ~37): Softer conventional foam, often used in quilting and low-density applications
- MW 3500 (OH ~32): Viscoelastic/memory foam base — slow recovery characteristic
- MW 4800–6000 (OH 28–35): High-resilience grades — excellent elasticity and durability
2.3 Functionality — How Many Arms?
Functionality refers to the average number of OH groups per molecule:
- f = 3 (triol): Standard for flexible foam — gives good crosslinking without brittleness
- f = 2 (diol): Used in elastomers and coatings where you want linear chains
- f > 3: Increases crosslinking density → firmer foam, may be used in semi-rigid applications
Most flexible foam polyols are triols initiated from glycerol or trimethylolpropane (TMP).
3. Common Polyether Polyol Grades and Their Applications
DL-2000D / PPG 2000 (MW 2000, OH ~56)
- Application: Conventional flexible slabstock foam for furniture, mattresses, carpet underlay
- Typical foam density: 16–35 kg/m³
- Partner isocyanate: TDI 80/20
- Processing: Wide processing window, forgiving formulation
View DL-2000D Product Details →
DEP-5631D (HR Polyol, MW ~5000, OH ~32)
- Application: High-resilience molded foam for automotive seating, premium furniture
- Typical foam density: 35–60 kg/m³
- Partner isocyanate: TDI 80/20 or MDI blend
- Processing: Requires tighter formulation control; often used with polymer polyol (SAN polyol) for load-bearing enhancement
View DEP-5631D Product Details →
DEP-3500D (Memory Foam Polyol, MW ~3500, OH ~160–180)
- Application: Viscoelastic (memory) foam for pillows, mattress toppers, ergonomic cushioning
- Typical foam density: 40–80 kg/m³
- Partner isocyanate: TDI 80/20 or MDI
- Processing: Sensitive to temperature during processing; slower cure than conventional foam
View DEP-3500D Product Details →
4. How to Read a Polyol COA (Certificate of Analysis)
When you receive a polyol shipment, check these values on the COA:
| Parameter | Typical Specification | What Deviation Means |
|---|---|---|
| OH Value | ±2 mg KOH/g of nominal | Changes crosslinking density → changes foam hardness |
| Acid Value | ≤ 0.05 mg KOH/g | Higher acidity consumes catalyst → slower reaction |
| Water Content | ≤ 0.05% | Excess water reacts with isocyanate → CO₂ bubbles → lower density |
| Viscosity at 25°C | Per grade spec | Higher viscosity → mixing difficulty |
| pH | 5.0–7.0 | Outside range → catalyst instability |
| Color (APHA) | ≤ 50 | Darker color may indicate oxidation or contamination |
| Unsaturation | ≤ 0.02 meq/g | Higher unsaturation → odor issues, foam scorching |
The most common quality issue: elevated water content. Even 0.1% extra water generates enough CO₂ to reduce foam density by 2–3 kg/m³.
5. Frequently Asked Questions
Q: What's the difference between polyether polyol and polyester polyol?
A: Polyether polyols have ether linkages (-C-O-C-) in the backbone; polyester polyols have ester linkages (-COO-). For flexible foam, polyether polyols dominate because they offer better hydrolysis resistance, lower viscosity, and wider processing windows. Polyester polyols are used where higher mechanical strength or solvent resistance is needed (e.g., shoe soles, some CASE applications).
Q: Can I use the same polyol for TDI and MDI formulations?
A: Generally yes, but you may need to adjust the index (NCO/OH ratio). TDI-based flexible foam typically runs at index 100–110; MDI-based foam runs higher (90–105 for flexible MDI systems). The reactivity profile differs — TDI systems have a more gradual rise, while MDI systems cure faster.
Q: How should polyether polyol be stored?
A: Store in sealed containers under nitrogen blanket at 15–35°C. Polyols are hygroscopic — they absorb moisture from air. Once a drum is opened, use within 1–2 weeks. Do not store near heat sources or in direct sunlight. Shelf life in original sealed packaging: 12 months.
Q: What is the typical MOQ for polyether polyol from China?
A: Standard MOQ is 1 FCL (16–23 metric tons, depending on specific gravity). Sample quantities (1–5 kg) are available for evaluation. Some specialty grades may have higher MOQs depending on production batch sizes.
Q: Does DOBO provide formulation support?
A: Yes. Our technical team can recommend the optimal polyol grade and provide starting formulations based on your target foam properties (density, hardness, resilience). Contact us with your specifications.
6. Quick Selection Checklist
Before placing your polyol order, confirm:
- □Target foam type (conventional / HR / memory / semi-rigid)
- □Target density range
- □Desired foam hardness (ILD/IFD value if known)
- □Isocyanate partner (TDI 80/20 or MDI)
- □Required OH value and acceptable tolerance
- □Packaging: 200kg drums, 1000kg IBC, or flexitank
- □COA required: OH value, acid value, water content, viscosity, pH, color
- □Shelf life and storage conditions at your facility
Conclusion
Choosing the right polyether polyol comes down to matching OH value, molecular weight, and functionality to your foam application. A methodical approach — starting with the target foam properties and working backward to polyol specifications — prevents costly formulation failures and production delays.
At DOBO Chemical, we supply a full range of polyether polyols from China's leading manufacturers:
- DL-2000D (PPG 2000) — Conventional flexible foam workhorse
- DEP-5631D — Premium high-resilience automotive-grade polyol
- DEP-3500D — Memory foam specialty polyol
- Rigid Foam Blended Polyol Systems — Ready-to-use for insulation applications
Every shipment includes a detailed COA. Free samples available for qualified buyers.
Need Help Selecting the Right Polyol?
Our technical team can recommend the optimal grade for your application