PU (Polyurethane) shoe soles are mainly made using these chemicals and raw materials:
Main PU Sole Chemicals
| Chemical | Function |
|---|---|
| Polyol | Main soft segment giving flexibility and cushioning |
| MDI (Methylene Diphenyl Diisocyanate) | Reacts with polyol to form polyurethane |
| TDI (Toluene Diisocyanate) | Alternative isocyanate in some formulations |
| Catalysts | Speed up PU reaction and curing |
| Blowing agents | Create foam/lightweight structure |
| Silicone surfactants | Stabilize foam cells |
| Pigments/Colorants | Add color to soles |
| Chain extenders (ethylene glycol, diethylene glycol) | Improve strength and elasticity |
| Release agents | Help remove soles from molds |
| Fillers (calcium carbonate, silica) | Reduce cost and modify hardness |
| Additives | Improve anti-slip, anti-static, UV resistance, hydrolysis resistance |
Common Chemicals Specifically Mentioned in PU Footwear
According to footwear PU manufacturing references, PU soles are commonly made using:
- Adipic acid
- MDI
- Diethylene glycol
- Ethylene glycol
- Auxiliary additives
PU Sole Production System
Most shoe factories use a 2-component PU system:
- Polyol component (A side)
- Isocyanate component (B side)
These are mixed and injected into molds where the PU expands and cures into the sole.
Additional Chemicals Used in PU Sole Factories
- Water-based or oil-based mold release agents
- PU sole paints and coatings
- Solvents
- Adhesives for bonding upper to sole
Properties of PU Soles
PU soles are popular because they are:
- Lightweight
- Flexible
- Shock absorbing
- Wear resistant
- Comfortable
But they can suffer from:
- Hydrolysis degradation (crumbling with age/moisture)
- Poor high-temperature resistance compared with rubber