What is a Carbon Fiber Tow?

Carbon Fiber Tow is the thread used to weave carbon fiber fabrics. As a standalone product, it can be used to make wound parts, pultrusion, or chopped as a local reinforcement. This 24K tow (or yarn) is composed of 24,000 individual carbon filaments, which boast the highest ultimate tensile strength in the industry.

What is a Spread Tow?

“Spread tow” refers to the practice of spreading a fiber into a thinner, flatter reinforcement, for example a 5-mm wide 12K Carbon Fiber Tow is commonly spread to a 12K Spread Tow 25-mm width Carbon Fiber tape.

The spread tow offers a smaller crimp angle than a standard tow weave and can decrease the crossover defects by increasing the smoothness. A lower crimp angle will result in higher strength as well as lower weight by reducing the excess resin that accumulates in crimps.

Since spread tow carbon fiber fabrics are extremely flat, they require less resin than traditional fabrics to be impregnated. This results in composites with a higher fiber-to-matrix volume ratio and overall better mechanical performances.

As an example, a typical 200 gsm 3K Plain Weave 50” wide fabric will have about 23,000 places where the weave overlaps, also called a crimp. Each crimp in the fabric has a very small area where excess resin will accumulate. By spreading the tow, the number of crimps is eliminated by over 90% which in turns eliminates the amount of area where excess resin can accumulate. In one yard of fabric you reduce over 21,000 of these super small resin pools yielding a part that is almost 20% lighter than a standard laminate.

Unidirectional Carbon Fiber

As the name implies, uni, meaning one, all of the fibers are oriented in the same direction. This gives uni-directional (UD) fabric some high strength benefits. UD fabric is not woven, there aren’t any interlacing fibers with crimping that can weaken the structure. Rather, there are continuous fibers that increase the strength and stiffness. Another benefit is the ability to tailor the layup with better control for performance characteristics. A bicycles frame is a good example of how UD fabric can be used to tune the performance. The frame must be stiff and rigid in the bottom bracket area to transfer the rider’s power to the wheels, but the frame also needs to have some compliance and flex to not beat up the rider. With UD material you can pick the precise direction of the fibers to get the strength you need.

One major drawback with UD though is its workability. UD tends to fall apart quite easily during the layup process since it has no interlaced fibers to hold it together. If the fibers are placed incorrectly it can be almost impossible to correctly reorient them all again. Machining parts made with UD fabric can also cause issues. If there is any fiber pull up where the features were cut, those loose fibers can pull up all the way across the part. Typically, if UD material is chosen for a layup, a layer of woven material is used for the first and last layer to assist with machineability and part durability.

1×1 Plain Weave

A plain weave carbon fiber sheet looks symmetrical with a small checkerboard style appearance. In this weave the tows are woven in an over/under pattern. The short space between interlaces give the plain weave a high level of stability. Fabrics stability is the ability for a fabric to maintain its weave angle and fiber orientation.  Due to this high level of stability, plain is not well suited for layups with complex contours, it will not be as pliable as some of the other weaves. Generally, plain weave fabrics are suited for flat sheets, tubes and 2D curves.

Also known as plain weave, this pattern resembles a math notebook. The over-under weave is a standard fabric pattern. Its quality might not be the strongest, but it is the easiest to handle. While other weaves are quicker to fall apart, the fibers of this pattern hold together efficiently.

2×2 Twill Weave

This pattern looks more modern than 1×1 plain pattern. Got quite unique look. It represents the diagonals that are synchronized. Is braid over-over-under-under. Most popular pattern that many carbon fiber factories use to make details. 2×2 Twill is mostly used in imitations also. This pattern is elastic and it is good for use with complex shapes because its weave is looser.

This pattern is elastic and it is good for use with complex shapes because its weave is looser.

4×4 Twill Weave

Quite fancy pattern, but not the fanciest. Pattern reminds arrows heads or tractor traces. Is not so prevalent pattern in the carbon fiber sheet market. 4X4 twill will bend around curves better than a 2X2 twill weave.

4X4 twill will bend around curves better than a 2X2 twill weave.

4 Harness Satin Weave

This pattern resembles a brick wall. Supposedly one of the strongest structural weaves. 4HS = 4 over 1.

This pattern resembles a brick wall.

5 Harness Satin Weave

5 Harness-Satin Carbon Fiber Pattern
Brotherto 4HS. A Harness-Satin pattern usually has more weaves per inch than a plain or twill weave (defined as “pics”). With its higher pic count, it will hold together better than a twill weave. Nevertheless, it should be handled carefully. 5HS = 5 over 1

8 Harness Satin Weave

Relative to 5HS. This original looking pattern resembles long rice grains. Should be handled carefully, as the weave is easy to fall apart. 8 Harness-Satin is the best choice for complex curves. 8HS = 8 over 1

Best choice for complex curves. 8HS = 8 over 1

12K Spread Tow Plain Weave

Based off the standard tow plain weave; a spread tow plain weave carbon fiber sheet looks symmetrical with a large checkerboard style appearance. In this weave the tows are woven in an over/under pattern. The short space between interlaces give the plain weave a high level of stability. Fabrics stability is the ability for a fabric to maintain its weave angle and fiber orientation.  Due to this high level of stability, plain is not well suited for layups with complex contours, it will not be as pliable as some of the other weaves. Generally, plain weave fabrics are suited for flat sheets, tubes and 2D curves.

12K Spread Tow Twill Weave

A twill weave carbon fiber sheet looks asymmetrical with a diagonal style appearance. In this weave the spread tows are woven in an over/under pattern. The short space between interlaces give the plain weave a high level of stability. Fabrics stability is the ability for a fabric to maintain its weave angle and fiber orientation.  Due to this high level of stability, plain is not well suited for layups with complex contours, it will not be as pliable as some of the other weaves. Generally, plain weave fabrics are suited for flat sheets, tubes and 2D curves.