Porosity

Porosity is the fraction of a material’s volume occupied by voids. In filtration it applies to both the clean medium (open area and tortuosity govern initial resistance) and the forming cake (porosity and compressibility determine ∆p rise, washing efficiency and achievable dryness). High porosity increases permeability at a given pore size, but if pore size distribution is broad it may also degrade cut‑off sharpness. For cakes, porosity evolves during consolidation and drying; compressible cakes lose porosity with rising pressure, increasing resistance. Measurement methods include gravimetric density, mercury intrusion (for rigid media) and flow‑based estimates via Darcy relations. Durable specifications couple porosity with MFPS, bubble point and permeability so that geometry and hydraulics are described consistently.