Air permeability is a concept that describes the ability of air to pass through fibers, yarns and fabric tissue. This concept also relates to the capture or transfer of air passing through the body. Air permeability varies depending on the properties and finishing processes of the fibers and yarns in the fabric texture. Air permeability decreases in humid, high pressure and hot weather conditions and increases in low pressure climatic conditions.

The air permeability of a fabric is influenced by fiber, yarn and fabric construction. For example, the permeability of fabrics woven from fine yarn and formed of low density is more permeable than that of a tightly woven fabric. A fabric completely woven with polyester double-ply yarn has poor air permeability. In contrast, the air permeability of the woven fabric is better with a mixture of 40 percent polyester and 60 percent cotton yarn.

In short, the higher the firmness, the higher the resistance of the fabric to the passage of air. Therefore, air permeability of loose and woven fabrics with fine yarn is high.

The air permeability of the fabric is important in maintaining the body's comfort and protection against moisture. The better the air permeability of the fabric, the more the air temperature circulating around and on the body is more easily transported outside the body. However, the fabric with low air permeability cuts air movement and prevents heat loss.

For physical tests performed in accredited laboratories, standards issued by local and foreign organizations are complied with. The standards applied in air permeability tests are as follows:

• TS 391 EN ISO 9237 Textile - Determination of air permeability in fabrics
• ASTM D737 Standard Test Method for Air Permeability of Textile Fabrics

These standards apply to textile products, fabrics, non-wovens (ie non-woven and knitted, specially manufactured for special uses and costly according to the duration of use) and garment textile products used in technical industry.