ISO 535 Cobb Test

Exposure Boundary

Variations in fibre composition or porosity influence how quickly moisture migrates through a sheet during this process. A low result indicates a high resistance to liquid penetration which works for high-end offset printing or moisture-sensitive carton applications. High values suggest a structure with open pores that might accommodate heavy saturating resins in later converting stages but perform poorly for sharp image reproduction.

The technique stops providing useful data when the water fully penetrates the thickness of the sample before the timer ends. When this saturation occurs, the mass gain represents the total capacity of the sheet rather than its resistance to surface wetting.

Performance Constraint

Precise control over blotting force and timing remains the primary factor for consistency across different laboratory environments. Any deviation in roller pressure alters the amount of water trapped in the fibre matrix which shifts the final mass reading. Standardized pads of filter paper prevent external moisture retention that might skew the outcome for lightweight grades.

Suppliers and converters use these verified increments to manage the interactions between stock properties and chemical coating applications. The measured values define the upper limit of water exposure a product tolerates before structural degradation occurs.