1. High Closed-Cell Ratio
- Polyol: high ethylene-oxide ratio and high activity, often after switching to a polyol of different activity.
- Recipe: too much stannous octoate, high isocyanate activity, high cross-linking density and speed, too much amine and physical blowing agent, or an over-high TDI index.
2. Shrinkage (gel speed higher than foaming speed)
- High closed-cell ratio causes shrinkage on cooling.
- Low air or material temperature.
- Excess silicone oil or physical blowing agent, or too low a TDI index.
3. Internal Cracking
- Low air temperature but high reaction-centre temperature.
- Low TDI index, too much tin, or high early foaming strength.
- High silicone-oil activity but low dosage.
4. Top Cracking (unbalanced gas-generation and gel speed)
- Low air or material temperature.
- Insufficient catalyst, too little amine, or poor silicone oil quality.
5. Bottom-Corner Cracking and Large Surface Cells
- Too much amine makes foaming too fast; excess physical blowing agent or poor silicone oil and catalyst cause large surface cells.
6. Poor Low-Temperature Performance
Poor intrinsic quality of the polyol: low functionality and high unsaturation at the same hydroxyl value, or a low TDI index at the same tin dosage.
7. Poor Air Permeability
- Low air temperature.
- High polyol and silicone-oil activity.
- Too much tin, or too little water and amine at the same tin dosage, or an over-high TDI index.
8. Poor Resilience
- High polyol activity, low molecular weight, or high silicone-oil activity.
- Too much silicone oil or tin, too much water at the same tin dosage, or an over-high TDI index.