Several factors can affect the air permeability of fabric. These factors include:
1. Fabric Structure: The structure and construction of the fabric play a significant role in determining its air permeability. Fabrics with a more open or loosely woven structure tend to have higher air permeability compared to tightly woven fabrics.
2. Fiber Type and Diameter: The type and diameter of the fibers used in the fabric can impact its air permeability. Fabrics made from finer fibers or fibers with irregular shapes generally exhibit lower air permeability due to reduced interstitial spaces for airflow.
3. Yarn Density: The density of yarns used in the fabric affects its air permeability. Higher yarn density, achieved through tighter packing of yarns, tends to reduce air permeability. Conversely, fabrics with lower yarn density allow more air to pass through.
4. Fabric Thickness: The thickness or thickness-to-weight ratio of the fabric influences its air permeability. Thicker fabrics typically have lower air permeability compared to thinner fabrics, as thicker materials provide more resistance to airflow.
5. Fabric Finishings: Chemical treatments or finishes applied to the fabric can alter its air permeability. Finishes like water repellents, coatings, or laminations may reduce air permeability by sealing the fabric's surface or filling gaps between fibers.
6. Moisture Content: Moisture or humidity levels can impact the air permeability of certain fabrics. Some fabrics may experience changes in their structure and dimensions when exposed to moisture, potentially affecting airflow and air permeability.
7. Pressure Differential: The difference in pressure on either side of the fabric affects its air permeability. Higher pressure differentials can increase the airflow through the fabric, resulting in higher air permeability.
8. Pore Size and Distribution: The size and distribution of pores or gaps within the fabric influence its air permeability. Fabrics with larger and more evenly distributed pores tend to have higher air permeability compared to fabrics with smaller or irregularly spaced pores.
It's important to note that these factors are interrelated, and their combined effects determine the overall air permeability of a fabric. Testing methods, such as ASTM D737 or ISO 9237, can be used to measure and quantify the air permeability of fabrics under standardized conditions.