Why are the length specifications for polyester staple fibers 32mm and 64mm?

Aug 18
4 min read

Updated: Sep 30

Polyester staple (single fiber) has a set standard such as 32mm, 64mm.

Then what criteria led to this standard?

In this post, we will introduce in detail how the cut length of polyester fiber is determined, its background, international standards, and uses by cut length.

Background on Cut Specifications for Polyester Fibers: A Historical Perspective

When synthetic fibers such as polyester were first commercialized, the global textile industry already had well-established infrastructure for cotton and wool spinning.

To promote the widespread use of synthetic fibers like polyester, they needed to be cut into lengths (staple form) that could be processed using existing spinning machinery.

The textile industry, which first developed in Europe, traditionally used the inch system.

As a result, staple fibers were commonly referred to as "1.5 inch" (approximately 38 mm), "2.0 inch" (51 mm), or "3 inch" (76 mm).

Today, however, the metric system is widely adopted worldwide, and these lengths are generally referred to as 38 mm, 51 mm, and 76 mm.

Ultimately, the cut lengths of polyester staple fibers were determined to match the length range of natural fibers like cotton. This was done to ensure compatibility with conventional spinning processes.

Background on cutting specifications for polyester fibers: International standards

There is no explicit “international standard” that strictly limits the length of polyester staple fibers. However, international standards do exist in terms of testing methods and terminology.

Organizations such as the International Organization for Standardization (ISO) and the American Society for Testing and Materials (ASTM) have established standards that focus more on measurement methods and quality criteria rather than restricting fiber length itself.

These international testing standards do not impose regulations like “polyester fibers must be cut to exactly 32 mm.” Instead, they serve to align the fiber lengths suggested by individual companies or national standards, enabling mutual compatibility.

In other words, although a “standard cut length = 38 mm” is not legally mandated on an international level, the establishment of standardized measurement methods and quality benchmarks by such organizations has led to the widespread adoption of common lengths such as 32 mm, 51 mm, and 64 mm within the industry.

Cutting length varies depending on the application

So, how does the application vary depending on the cut length?

The optimal cut length of polyester staple fiber varies depending on its end use and the type of spinning or nonwoven process applied. Below is a summary of typical fiber lengths by application and the reasons behind them:

Staple fibers for cotton spinning : Fibers with a length of approximately 30–40 mm (e.g., 32 mm, 38 mm) are commonly used.
This range is optimized for the fiber length that cotton spinning systems can handle. Since the typical fiber length of cotton is around 20–30 mm (with long-staple cotton reaching 30–40 mm), polyester is cut to a similar or slightly longer length to facilitate easy blending and spinning.

Staple fibers for wool spinning : Fibers with lengths of approximately 50–75 mm (e.g., 51 mm, 64 mm) are commonly used, and in some cases, even longer fibers are applied. Wool fibers are longer than cotton fibers, and processes such as worsted or woolen spinning are designed to handle long fibers. Accordingly, polyester is also supplied in longer cut lengths—often referred to as "wool-type" staple fibers—to suit these applications.

Fibers for nonwoven fabrics : In nonwoven production, the appropriate fiber length varies significantly depending on the manufacturing process.

For processes like wet-laid or air-laid, where fibers are dispersed in water or air to form a thin web, very short fibers are required to achieve a uniform sheet. In such cases, ultra-short fibers such as 6 mm or 12 mm are used. In the industry, fibers of 3 mm, 6 mm, and 12 mm are generally classified as ultra-short fibers.

In contrast, spunlace processes use carding to form the web. If the fibers are too short, they do not entangle properly, resulting in weak web strength. Therefore, medium-length fibers of around 38–51 mm are commonly used, and in some cases, 64 mm fibers are also applied.

Fibers for filling materials: Polyester staple fibers are widely used as filling materials for items such as comforters, pillows, and cushions. In filling applications, longer fibers generally provide better loft and resilience. Therefore, relatively long fibers—typically around 64 mm or 76 mm—are preferred.

Application	Typical Length (mm)	Reason
Cotton Spinning	32–38	Suitable for blending with cotton fibers (20–30 mm)
Wool Spinning	51–76	Longer than wool, excellent for blending and yarn quality
Nonwoven	6–12 / 38–51	Ultra-short fibers for wet-laid; mid-length for carded web (spunlace)
Filling Material	64–76	Long fibers for enhanced loft and resilience

Long fibers offer advantages in terms of strength but may increase the risk of spinning defects. Short fibers are more difficult to spin but blend well with natural fibers and can enhance production speed. Each type has its own advantages and disadvantages.

Taking these factors into account, the global textile industry has adopted standard fiber lengths—such as 32/38 mm and 51/64 mm—as common practice. International standardization organizations and national regulations support this by providing guidelines for measurement and classification.

At DK FIBER, we supply polyester staple fibers in a wide range of lengths and are fully prepared to provide customized fiber specifications to meet your needs.