What Is Carbon Fiber Cloth?

Carbon Fiber Spoiler
Carbon Fiber Spoiler. Todd Johnson

Carbon fiber is the backbone of lightweight composites. Understanding what carbon fiber cloth is required knowing the manufacturing process and composite industry terminology. Below you will find information on carbon fiber cloth and what the different product codes and styles mean.

Carbon Fiber Strength

It needs to be understood that all carbon fiber is not equal. When the carbon is manufactured into fibers, special additives and elements are introduced to increase strength properties.

The primary strength property that carbon fiber is judged upon, is modulus

Carbon is manufactured into tiny fibers through either the PAN or Pitch process. The carbon is manufactured in bundles of thousands of tiny filaments and wound onto a roll or bobbin. There are three major categories of raw carbon fiber:

  • High Modulus Carbon Fiber (Aerospace Grade)
  • Intermediate Modulus Carbon Fiber
  • Standard Modulus Carbon Fiber (Commercial Grade)

Although we might come in contact with aerospace grade carbon fiber on an aircraft, such as the new 787 Dreamliner, or see it in a Formula 1 car on TV; the majority of us will likely come in contact with commercial grade carbon fiber more frequently.

Common uses of commercial grade carbon fiber include:

  • Sporting goods
  • Car hoods and aftermarket parts
  • Accessories, like iPhone cases

Each manufacturer of raw carbon fibers has their own nomenclature of the grade. For example, Toray Carbon Fiber calls their commercial grade "T300," while Hexcel's commercial grade is called "AS4."

Carbon Fiber Thickness

As previously mentioned, raw carbon fiber is manufactured in tiny filaments (around 7 microns), these filaments are bundled into rovings which are wound onto spools. The spools of fiber are later used directly in processes like pultrusion or filament winding, or they can be woven into fabrics.

These carbon fiber rovings are comprised of thousands of filaments and are almost always a standard amount. These are:

  • 1,000 c (1k carbon fiber)
  • 3,000 filaments (3k carbon fiber)
  • 6,000 filaments (6k carbon fiber)
  • 12,000 filaments (12k carbon fiber)

This is why if you hear an industry professional talking about carbon fiber, they might say, "I am using a 3k T300 plain weave fabric." Well, now you will know that they are using a carbon fiber fabric that is woven with Toray standard modulus CF fiber, and it is using fiber that has 3,000 filaments per strand.

It should go without saying then, that the thickness of a 12k carbon fiber roving will be twice that of a 6k, four times as a 3k, etc. Due to efficiencies in manufacturing, a thicker roving with more filaments, such as a 12k strand, is usually less expensive per pound than a 3k of equal modulus.

Carbon Fiber Cloth

Spools of carbon fiber are taken to a weaving loom, where the fibers are then woven into fabrics. The two most common types of weaves are "plain weave" and "twill." Plain weave is a balanced checker board pattern, where each strand goes over then under each strand in the opposite direction. Whereas a twill weave looks like a wicker basket.

Here, each strand goes over one opposing strand, then under two.

Both twill and plain weaves have an equal amount of carbon fiber going each direction, and their strengths will be very similar. The difference is primarily an aesthetic appearance.

Every company that weaves carbon fiber fabrics will have their own terminology. For example, a 3k plain weave by Hexcel is called "HexForce 282," and is commonly called "282" (two eighty-two) for short. This fabric has 12 strands of 3k carbon fiber per inch, in each direction.