Blindness in Polyurethane Foam
Blindness — sometimes called closed-cell pockets or glass — appears when regions of foam that should be open-celled fail to open during cure. The result is reduced airflow, inconsistent hand-feel, and parts that don't pass quality testing. The defect is often invisible until the foam is cut.
Common root causes include catalyst imbalance between gel and blow reactions, surfactant level or grade mismatch, isocyanate index drift, raw material batch variation (particularly polyol moisture and OHV), process temperature or humidity changes, and mixing efficiency issues. By the time blindness shows up on the line, two or three small drifts have usually combined.
First-line checks: cross-section the bun at multiple points, run airflow tests on affected vs known-good zones, pull recent CoAs for polyol/iso/surfactant, compare current reactivity profile against the reference formulation, and review ambient and material temperature logs.
Diagnosing blindness on a specific line requires looking at formulation, raw material data, and process conditions together. We help foam producers do this kind of forensic work every week.