Splits & Cracks in Flexible Foam
Splits and cracks running through a slabstock bun are one of the most visible foam defects — and one of the costliest, because the affected zones usually have to be cut out and scrapped. Most splits trace back to reaction profile and rise dynamics, not raw materials.
Common causes include isocyanate index too high or too low, catalyst imbalance favouring gel over blow, reaction profile that is too fast, insufficient surfactant, conveyor or paper temperature issues, and mixing or metering inconsistencies.
Where the splits appear matters: top splits often indicate index issues, centre splits often indicate exotherm or reactivity problems, edge splits often indicate temperature or surfactant. Documenting the location is the first diagnostic step.
First-line checks: re-measure your reactivity profile and compare against reference values, recalculate the isocyanate index using current OHV and water content from CoAs, check conveyor and paper temperature logs, inspect mixhead and metering condition, and review any recent change in raw materials or environment.