porousness

Porousness is the quality or condition of containing pores, that is, voids within a material. In scientific usage it is often described using porosity, the fraction of a material's volume occupied by pore space. Porosity is a dimensionless quantity usually expressed as a percentage or decimal between 0 and 1. Porous materials may have open porosity, where pore spaces are interconnected and allow fluids or gases to move through, or closed porosity, where pores are isolated and do not contribute to flow. Porousness influences mechanical, thermal, and transport properties, sometimes in contrasting ways; higher porosity can reduce strength but increase storage capacity or permeability.

Porosity is distinct from permeability, which measures the ease with which fluids pass through a material's pore network. Porousness also depends on pore size distribution, connectivity, and tortuosity (the winding path through pores). The pore walls' surface area relative to volume is another important factor, affecting reactions, adsorption, and heat transfer.

Measurement techniques include mercury intrusion porosimetry, gas adsorption methods such as BET analysis, imaging by micro-computed tomography, and helium or mercury pycnometry for skeletal density. Porosity is commonly used in soils, rocks, ceramics, foams, membranes, and porous polymers.

Applications encompass filtration, catalysis, battery separators, insulation, acoustic damping, tissue engineering scaffolds, and oil and gas reservoir evaluation. Designers balance porosity against mechanical strength, durability, and permeability according to the intended use.