How to Classify Large and Small Carbon Fiber Tows and Comparative Performance Analysis

2025-09-13 14:49:44

Carbon fiber products offer exceptionally high material properties, including lightweight, high strength, and corrosion and wear resistance far exceeding comparable metal products. Consequently, they are widely used in many fields and industries. A key factor influencing the performance of carbon fiber products is the tow rating. These are often referred to as large tow and small tow. For those unfamiliar with the concept, it can be difficult to determine the type of carbon fiber tow (or raw material) needed for their product. This article will discuss how to classify large and small carbon fiber tows and their performance characteristics.

How to Classify Large and Small Carbon Fiber Tows

First, understand that each carbon fiber strand is 5 to 10 microns thick, much thinner than a human hair. Therefore, the carbon fiber we see is actually composed of several strands. Commonly used parameters for carbon fiber tow ratings include 3k and 12k. The k here stands for 1,000, so 3k represents 3,000 carbon fiber strands. 12k carbon fiber tow is four times thicker than 3k carbon fiber. When combined with resin to form prepreg tape, ignoring the impregnation effect, the performance of 12k carbon fiber material is far superior to that of 3k carbon fiber.

The distinction between small-tow and large-tow carbon fiber is simply a categorization within the industry based on the number of carbon fiber filaments. Carbon filaments below 24k are considered small-tow, while carbon filaments above 24k are considered large-tow. By now, I believe everyone understands the distinction between large-tow and small-tow carbon fiber. As large-tow carbon fiber research and development continues to improve, I believe this distinction will continue to evolve.

Because small-tow carbon fiber has fewer carbon filaments, it's easier to fuse with resin, making product performance more manageable. Many products currently use small-tow carbon fiber raw materials. Large-tow, however, has more filaments, requiring manufacturers to meet higher performance requirements and resulting in higher raw material and process costs. Therefore, it's typically used in high-end industries.

Performance Comparison of Large and Small Carbon Fiber Tows

After reviewing the above classification of large and small carbon fiber tows, what about the performance of large and small carbon fiber tows? As can be seen above, large tows contain more carbon fiber filaments. So, as reinforcement in carbon fiber composites, more carbon fiber filaments necessarily mean better performance. Is this a simple conclusion? Obviously not, as there are many processes involved. When comparing the performance of large and small tows, we actually need to consider three aspects.

1. Carbon Fiber Tow Sizing Rate

After production, carbon fiber filaments are pre-baked before sizing. Then, they are sizing liquid. The higher the sizing rate, the better the performance of the carbon fiber filaments. The results show that large tow carbon fiber has a higher sizing rate, while small tow carbon fiber has a lower sizing rate. Therefore, from a raw yarn perspective, large tow carbon fiber has higher performance than small tow carbon fiber.

2. Single Filament Strength

Because the external parameters of large tow carbon fiber are more stable, while those of small tow carbon fiber are less stable, small tow carbon fiber experiences greater changes under stress, resulting in higher performance of small tow carbon fiber.

3. Shear Strength

Shear strength also reflects the tensile strength of subsequent carbon fiber products. In this regard, the shear strength of large-tow carbon fiber resin is lower than that of small-tow carbon fiber. This is easy to understand. Currently, large-tow carbon fiber impregnation is not as thorough as that of small-tow carbon fiber. In other words, the resin doesn't bond each filament during impregnation, which can easily lead to greater stress when subjected to external forces. Many manufacturers currently developing thermoplastic carbon fiber prepreg tapes are unable to complete their development due to the low fluidity of the thermoplastic resin and the resulting suboptimal impregnation.

Currently, small-tow carbon fiber offers superior performance, which explains its widespread application. Large-tow carbon fiber is currently more expensive and rarely adopted by customers. However, as technology continues to evolve and mature, I believe that large-tow carbon fiber will undoubtedly offer even higher product performance. Carbon fiber products produced with large-tow carbon fiber, which has a higher sizing rate, will also exhibit stronger performance.