We are going to learn about air permeability, its importance and the factors that affect airflow through textiles; lab testing methods; international standards; and practical tips for improving the comfort, breathability and performance of the fabric.
Pores of the fabric which increases or decreases the air permeabilityIntroduction to Air Permeability
Air permeability is one of the most important physical properties used to evaluate the performance of textile fabrics, and it determines how easily the air passes through a fabric and influences the comfort, thermal insulation, ventilation and overall performance of the product. A fabric that allows sufficient airflow keeps the wearer cool and comfortable, while a garment with lower air permeability provides better protection against wind and heat loss. So we can say that manufacturers make the fabric keeping the end use in mind.
What Is Fabric Air Permeability?
Air permeability of a fabric is its ability to allow air to pass through its structure under a specified pressure difference. During testing, a controlled air pressure is applied to one side of the specimen, and the volume of air passing through it is measured. A fabric with larger, more connected pores allows air to flow more easily, and vice versa.
Why Is Air Permeability Important?
The importance of air permeability depends entirely on the fabric’s end use. For sportswear and summer clothing, the highest air permeability improves ventilation by allowing body heat and sweat moisture to escape, which helps maintain a comfortable microclimate between the skin and the garment during any type of physical activity. The winter jackets and windproof garments require lower air permeability, which helps retain warm air around the body and prevents cold wind from penetrating the fabric, improving thermal insulation.
We know that each textile product has different performance requirements, so manufacturers must carefully control air permeability during design and production.
Factor Affecting Fabric Air Permeability
Fiber Characteristic
The nature of the fiber affects the airflow, as natural fibers such as cotton and linen have irregular cross-section shapes, such as amorphous and crystalline in cotton, creating small air spaces when spun into any type of yarn, while the synthetic fibers are generally uniform and specially engineered fibers that can improve the airflow, and the fineness of the fiber is also an important factor. Coarser yarn creates larger pores, while finer yarn packs together more tightly, reducing air passage.
Yarn Construction
High twist and low twist yarnHigher twist in the yarn creates compactness, which reduces the space available for airflow and vice versa. It has been demonstrated that two fabrics made of the same fiber exhibit different air permeability due to differences in yarn construction.
Fabric Structure
The construction of the textile product has the greatest influence on air permeability, as plain-weave cotton has a higher number of yarn interlacements, producing a compact structure with relatively low airflow. Twill weave has fewer interlacements, allowing slightly more air movement. Satin weave has long-yarn floats and fewer crossover points, creating larger openings that increase air permeability. Knitted fabric usually exhibits higher air permeability than all types of woven fabric due to its looped structure.
Construction of the woven and knitted fabricFabric Density
We know that the density is commonly expressed as End Per Inch (EPI) and Picks Per Inch (PPI).
As density increases, the space between yarns decreases, reducing the air permeability and vice versa. In our testing lab, we found an interesting point: two different fabrics with the same GSM can produce very different air permeability results, and that GSM measures fabric weight rather than pore structure.
Dyeing and Finishing
Different types of finishing, including chemical and mechanical processes, can alter the permeability of the fabric, and processes such as coating, lamination and calendaring compress the fabric’s structure, which reduces airflow. On the other hand, enzyme washing and many other finishing treatments slightly increase air permeability by altering the fabric’s surface.
How Is Air Permeability Tested?
Almost all testing procedures include:
- Condition the testing specimen under standard atmospheric conditions
- Mounting the testing specimen securely to prevent air leakage on the testing instrument
- Applying the specified pressure as per the applied testing standard
- The advanced instruments measure the airflow passing through the testing specimen
- Repeat the testing at different locations of the testing specimen and take the average reading
The modern Darong Air Permeability Testers are designed to perform these measurements in accordance with the selected testing standard, and they feature automatic pressure control, digital airflow measurement and user-friendly operation, helping the lab achieve consistent, repeatable results.
Darong advanced air permeability testerDemonstration of Air Permeability Testing.
International Testing Standards for Air Permeability Testing
Lab technician select the testing standards as per the requirements of the customer, and some internationally recognized standards are:
- ISO 9237 (Determines the air permeability of textile fabrics
- ASTM D737 (Standard test method for air permeability of textile fabrics
- GB/T 5453 (Chinese standards for textile air permeability
- JIS L1096 (Japanese testing method)
- BS 5636 (British standard for air permeability testing)
Common Manufacturing Problem
There are many production issues that can reduce the air permeability without being visible, and some common causes include:
- Excessive density of the fabric
- Incorrect yarn selection
- Extra compression during the finishing process
- Heavy coating or lamination
- Excessive shrinkage of the fabric
- Inconsistent weaving of knitting parameters
- Poor process control
Practical Tips for Manufacturers
The textile manufacturers can improve the air consistency of air permeability by:
- Select fibers that are suitable for the intended application
- Optimize the twist of the yarn and the construction of the fabric
- Control both EPI and PPI during production
- Monitor the finishing parameters carefully
- Proper conditioning of the testing specimen before lab evaluation
- Calibration of the testing instrument should be regularly performed
Conclusion
Air permeability is one of the most important properties that influence textile comfort, thermal regulation and functional performance, and it depends entirely on the combined effects of fiber characteristics, yarn construction, fabric structure, density and finishing processes. By understanding the principles of air movement through fabrics and performing standardized lab testing, textile manufacturers can improve production quality, ensure compliance with international standards and consistently deliver fabric that provides the desired balance of comfort, protection and durability.
FAQs
Is higher air permeability always better?
The simple answer is No. We know that higher air permeability improves ventilation but decreases wind resistance, and the ideal air permeability depends entirely on the intended use of the fabric.
Which fabrics usually have the highest air permeability?
Lightweight knitted fabrics, mesh fabrics and loosely woven textiles generally provide the highest airflow.
Does the higher GSM always mean lower air permeability?
No, GSM measures the weight of the fabric, and even fabrics with identical GSM can have very different air permeability because of the fabric’s construction; yarn properties and finishing also influence airflow.
Can finishing treatment change air permeability?
Yes. Different processes such as coating, lamination, brushing and calendaring can increase or decrease the air permeability depending on how they modify the fabric structure.
Related Resources
Insights and Experience on ISO 9237 Fabric Air Permeability Test
ASTM D737: Practical Tips on Air Permeability of Textile Fabrics Test Method