What is Textile Air Permeability and how to test

Definition of Textile Air Permeability

Textile air permeability is the ability of a fabric to allow air to pass through it under a specific pressure differential. This property determines how easily air can circulate through the fabric, affecting comfort and performance in various applications. Air permeability is an essential characteristic of textile materials used in products such as clothing, medical textiles, filters, tents, and sails.

Importance of Textile Air Permeability

Air permeability plays a crucial role in determining the suitability of fabrics for specific end uses. In clothing, fabrics with high air permeabilities are favored for summer wear. This is because fabrics with high air permeabilities enable enhanced heat dissipation and efficient moisture evaporation from the skin surface, unlike fabrics with lower levels of air permeability. Consequently, they provide greater comfort in regulating body temperature. Similarly, in medical textiles, it is crucial to maintain controlled airflow levels. This helps to promote effective wound healing and prevents infections by reducing bacterial growth on the skin surface. This is achieved by reducing bacterial growth on the skin surface.

In addition to its significant influence on product performance and comfort properties, the measurement of textile air permeability offers valuable insights into fabric quality control throughout the manufacturing processes. By assessing changes in this property over time, such as during production runs or after exposure to environmental conditions like washing or aging tests, manufacturers can effectively identify any defects that could potentially impact the final product’s quality. This enables proactive measures to be taken to rectify such issues and ensure consistent and satisfactory fabric quality.

Understanding textile air permeability is essential for anyone working with textiles in research or manufacturing environments. It enables them to evaluate and optimize material properties based on their intended use while ensuring consistency and reliability across different batches produced over time.

Factors affecting fabric permeability:

The air permeability of a fabric is influenced by various factors. These factors include the size of the fabric’s pores, their connectivity, the length and arrangement of channels within the fabric, surface traits, the volume fraction, and the fabric’s thickness. Additionally, environmental conditions such as temperature, humidity, and air pressure differences also play a role in affecting fabric air permeability.More importantly, it is related to the distribution characteristics of the pore size of the fabric.

Fabric structure:

In the same arrangement density and tightness conditions, different tissue structures of the strength of the air permeability in the order of plain < twill < satin < porous tissue.

This phenomenon can be attributed to the fact that fabrics with the same structure and thickness exhibit distinct characteristics. In particular, plain fabric stands out due to its higher number of interweavings in both the warp and weft directions. As a result, the pores between the yarns are smaller, thereby resulting in minimal air permeability. Conversely, perforated fabric features larger gaps between the yarns, leading to a more pronounced air permeability.

Within a specific range, increasing the twist of the yarn reduces the yarn diameter and fabric tightness, thereby enhancing the fabric’s breathability. Additionally, the smaller the volume fraction of the fabric, the better its air permeability. When the warp and weft yarn density remains unchanged but the arrangement density increases, the air permeability weakens.

Fiber properties:

Fiber with the increase in moisture regain rate, the breathability will be significantly reduced. Breathable performance hemp > cotton > wool > polyester > nylon fiber the shorter. The greater the rigidity, the greater the probability of generating hairiness, the more blocking and channel changes formed, and the worse the breathability.

Yarn structure: The denser the yarn structure, the smaller the intra-yarn permeability and the greater the inter-yarn permeability. The twist and finish of the yarn are beneficial to the permeability.

Environmental conditions significantly influence fabric permeability. Specifically, at specific temperatures, fabric permeability decreases as relative air humidity rises. This reduction in fabric permeability is attributed to the absorption of water by the fabric, causing fiber expansion and contraction. As a result, the internal pores within the fabric diminish in size. Furthermore, moisture that adheres to the fabric can obstruct the fabric pores, resulting in a decline in overall fabric breathability. Similarly, when relative humidity reaches a certain level, fabric air permeability decreases with increasing ambient temperature.

Types of Textile Air Permeability Testing Methods

Air permeability is a crucial property of textiles that impacts their performance and functionality. Various testing methods are available to measure textile air permeability, each with advantages and disadvantages. This section will discuss some of the most common testing methods used in textile laboratories.

1. Gurley Method

The Gurley method is one of the oldest and most widely used methods for measuring air permeability in textiles. It involves applying a steady pressure differential across a fabric sample and measuring the time a specific air volume takes to pass through it.

Advantages:

Simple procedure

Low-cost equipment

Suitable for low-permeability fabrics

Disadvantages:

Only suitable for non-woven fabrics

Temperature and humidity variations affects results.

2.Frazier Method

The Frazier method is another popular technique for measuring air permeability in textiles that involves forcing a controlled amount of air through the sample using negative pressure. Measure the airflow rate using an anemometer or any other similar device.

Advantages:

It is applicable to both woven and non-woven fabrics.

Provides accurate results even at meager airflow rates 

Disadvantages:

This method requires relatively expensive equipment such as an anemometer or manometer.

Preparation time can take longer than other methods.

3.Pressure Differential Flow Method

The pressure differential flow method measures the resistance material offers while allowing compressed gas (usually nitrogen) to flow through it under specified conditions from the high-pressure side to the low-pressure side.

Advantages: 

Accurate results over a wide range of pressures up to 7 bar.

Applicable on any kind/shape/thickness samples

Disadvantages: 

Measurements require a high level of technical expertise.

Expensive equipment setup.

4.Air Permeability Tester

An automated tester that uses digital readouts allows users better control over test times, pressures, volumes, etc. 

Advantages:

Automated testing for time-saving and accuracy.

It gives an average of multiple tests on the same sample 

Disadvantages:

Expensive equipment

It needs high technical expertise to operate.

It is essential to choose the suitable method based on the specific needs of your textile application. By knowing the advantages and disadvantages of each test, you can make a more informed decision about which method will be most effective for your material.

Industry Standards for Textile Air Permeability Testing

Textile manufacturers must follow industry standards and regulations when conducting laboratory air permeability testing. The two primary organizations that set these standards are the American Society for Testing and Materials (ASTM) and the International Organization for Standardization (ISO). 

The ASTM has developed several test methods related to air permeability, including D737-04(2018) Standard Test Method for Air Permeability of Textile Fabrics, which outlines procedures for measuring airflow rate through fabrics under specified conditions. This method includes guidelines on how to prepare samples, set up equipment, and calculate results. Other ASTM standards related to air permeability include D4491-20 Standard Test Methods for Water Permeability of Geotextiles by Permittivity and D3574-16e1 Standard Test Methods for Flexible Cellular Materials—Slab, Bonded, and Molded Urethane Foams.

Meanwhile, it is noteworthy that ISO has established several international textile air permeability testing standards.. These include ISO 9237:1995 Textiles – Determination of the permeability of fabrics to air; ISO 7231:2009 Leather — Physical tests — Determination of thickness, and many others.

To ensure precise and reliable outcomes while adhering to regulatory requirements, manufacturers should utilize these standardized methods when conducting air permeability tests in their laboratories. By following these established protocols, they can obtain consistent and comparable results, enabling effective quality control and assessment of fabric air permeability. Adhering to such protocols helps ensure quality control and provides a level playing field across all companies within the industry.

DaRong’s Air Permeability Tester products:

DaRong developped several models of Air Permeability Testers to meet different needs of clients. Let’s introduce DaRong’s hot product YG(B)461G fabric air permeability tester. This equipment can test the air permeability of fabrics, nonwovens, coated textiles, and other industrial papers (air filter paper, cement bag paper, industrial filter paper), leathers, plastics, and chemical products that require air permeability control.

Equipment technical parameters:

Pressure difference range: 1-4000.0Pa

Measurable air permeability: 0-12000mm / s (20cm²)

Measurable fabric thickness ≤ 10mm

Test area: 20cm²; 5cm²; 50cm²; 100cm²; Ф50mm (≈19.6cm²); Ф70mm (≈38.5cm²)

Air Permeability Tester
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