A good air permeability value for fabric depends on its specific application and requirements. Air permeability refers to the ability of a fabric to allow air to pass through it. Different fabrics have different air permeability levels, and the desired value will vary based on the intended use of the fabric.

For example, in certain applications like outdoor sportswear or activewear, a higher air permeability value may be desired to promote breathability and comfort. In contrast, for applications like protective clothing or upholstery, a lower air permeability value may be preferred for better insulation or barrier properties.

Air permeability is commonly measured using units such as cubic feet per minute (CFM) or liters per square meter per second (L/m²/s). However, there is no universally defined range for what constitutes a "good" air permeability value as it heavily depends on the specific fabric's desired performance and the requirements of the application.

To determine a suitable air permeability value for a fabric, it is important to consider factors such as:

1. Application: Identify the intended use of the fabric (e.g., apparel, home textiles, industrial applications) and understand the airflow requirements for that particular application.

2. Comfort: For clothing or bedding applications, consider the desired level of breathability and comfort. Fabrics with higher air permeability values may provide better moisture management and ventilation.

3. Functionality: Assess the functional requirements of the fabric, such as barrier properties, wind resistance, or insulation. In some cases, lower air permeability may be beneficial to maintain specific performance characteristics.

4. Standards and regulations: Check if there are any industry-specific standards or regulations that define the acceptable air permeability range for the intended application.

It's important to note that air permeability is just one aspect of fabric performance, and a comprehensive understanding of other factors such as strength, durability, and aesthetics is necessary when evaluating fabric suitability.

To obtain specific air permeability values for a particular fabric, it is recommended to consult fabric manufacturers, conduct standardized testing according to relevant testing methods (e.g., ASTM D737 or ISO 9237), or refer to industry-specific guidelines or standards. The desired air permeability value will vary based on the specific requirements and goals of the fabric application.