Carbon Weight and Weave Breakdown

When designing or manufacturing a carbon fiber component, several factors must be considered, including the weave type, fabric weight, and the strength characteristics of each layer. The following provides an overview of some of the most common carbon fiber materials and terminology used within the industry.

Terms

GSM (Grams per Square Meter) or OZ (Ounce Per Square Yard)

           -GSM (Or OZ) is the standard unit used in the textiles industry. It tells you how many grams a single sheet of fabric that is one meter long and one meter wide weighs. In the composite industry this along with Tow thread count, helps define the thickness and weight of a given material, and can also help determine the final weight of a finished part when all layers are added.

Warp and Weft

           Warp – Warp in a woven fabric refers to the fabric strand that runs in the longitude or vertical direction and is the strand that is held in tension while the horizontal (Weft) strand is woven into the fabric. Given this tension, a tow in the Warp direction is considered stronger than in the Weft direction.

           Weft – Weft in a woven fabric is the tow run in the horizontal direction. While the warp strand is held in tension the weft is woven in the desired pattern and generally is not under tension.

Tow

           Tow refers to the thousands of individual carbon fiber filaments bundled together to create one larger strand. Each tow consists of a pre determined number of filaments, commonly grouped in bundles of 1K, 3K, 6K, or 12K.

Crimp

           Crimp refers to the bend or waviness introduced into individual tows as they are interlaced over and under adjacent strands within a woven fabric. This waviness causes fibers to deviate from the primary load direction, reducing their ability to carry stress efficiently. In general, fabrics with a higher number of crimps exhibit lower overall strength and stiffness in a composite layup, as the fibers are less aligned and experience higher internal shear under load.

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Types of Carbon Fiber Weave

Plain weave

Plain weave looks similar to a checkerboard pattern with an even distribution of 1x1 (Over 1 / Under 1) weaves in the warp and weft directions. This is a very stable weave suitable for flat surfaces, however given this stability it will not be as pliable in complex shapes. Another downside of plain weave is the increased number of crimps in the weave, making sharper turns between interlaced tows causing it to have reduced strength.

2x2 Twill Weave

Twill weave is the most common woven fabric found in composites, given its balance between stability and strength as well as providing the signature chevron look carbon fiber is known for. Twill weave consists of a 2x2 (Over 2 / Under 2) weave pattern in the warp and weft direction, this allows for good stability while reducing the angle of crimping between interlaced tows. Though less common, twill can also be found in a 4x4 (Over 4 / Under 4) pattern slightly increasing strength and pliability while reducing stability.

Harness Satin Weave

Harness satin weave is the least stable of the common carbon fiber fabric weaves but also the most pliable, offering increased strength due to the reduced number of crimps between interlaced tows. It is typically denoted as 4HS, 5HS, or 8HS, where the number indicates the over/under pattern—4x1, 5x1, or 8x1 respectively. A higher number corresponds to fewer interlacings per tow, resulting in a more pliable fabric that conforms easily to complex shapes. However, this also reduces weave stability, making the material more prone to distortion during handling or layup.

Uni-directional (UD)

Unidirectional is simply a fabric with all fibers running in a single direction, held together by a carrier. UD is considered the strongest application of carbon fiber given it has no crimp along each strand, however is difficult to handle without the fibers coming loose. Uni-directional is extremely useful to engineers looking to increase strength in one direction, without over stiffening another in a given area, as stiffness is only increased along the length of the fiber. A downside of UD is that it is more prone to delamination. This is because it does not have the excess build-up of resin found in the cross-weaving of fibers that helps keep layers together.

Spread Tow

A fabric utilizing spread tow consists of flattening the bundle of filaments out into a wider strand, reducing its thickness and therefore reducing the severity of each crimp in the weave. With this technique it is possible to achieve a significantly stronger part, due to the reduced crimp and allowing more layers to be applied, increasing fiber content in a given area. This is a good compromise between the strength properties of unidirectional and the stability and workability of a woven fabric.

Chopped Strand or “Forged Carbon”

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With the growing popularity of carbon fiber—both for its structural performance and aesthetic appeal—manufacturers have developed a wider range of weave types to achieve unique visual effects and simplify production for recreational or consumer applications. One increasingly common approach involves using chopped strands of carbon fiber distributed randomly across a mold surface. This process creates a distinctive, marbled appearance and offers excellent formability, as the material easily conforms to complex shapes. However, because the fiber orientation and distribution are uncontrolled, the resulting composite has less predictable and generally lower directional strength compared to traditional woven or unidirectional carbon fabrics.

Structurally, chopped strand composites can still be effective when densely compacted, as in compression molding processes, where they provide uniform load distribution and good toughness. While not ideal for applications requiring maximum tensile or flexural strength, “forged carbon” offers a balance of formability, durability, and distinctive aesthetics—making it well-suited for components where both appearance and moderate mechanical performance are desired.

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Material References

The following are references found in the composites industry when looking at materials available and assist in planning a layup to maximize thickness, strength and weight.  

Filament count (K)

The “K” found in a material reference code describes the number of thousands of individual filaments found in a bundled strand of carbon fiber referred to as a “Tow”. Common counts include 1K, 3K, 6K, or 12K and these refer to how many thousand individual filaments are found, 1000, 3000 etc.

Material weight (GSM)

Another measurement required to properly understand what material you are working with is the GSM or “Grams per square meter”. A few common weights can include: 200gsm, 400gsm 660gsm. 200gsm implies that in a square meter of material it will weigh 200 grams, this combined with thread count can tell you the thickness of a material and its estimated weight in a layup.

Resin Content

Another reference found in prepreg is the resin content, displayed as a percentage of the GSM of a fabric. In prepregs this value is commonly in the 40% range and can vary given the material thickness or application.

Filament Strength

When selecting a carbon fiber fabric, references are often made to the strength of individual filaments, typically indicated by a grade designation. In the case of Toray fibers, for example, common grades include T300, T700, and T1100. These classifications represent different tensile strength levels, with higher numbers generally indicating stronger fibers. For instance, T300 is a standard-modulus material known for its affordability and versatility; T700 is an intermediate-modulus fiber widely used in industrial and recreational applications; and T1100 is an ultra-high-strength grade reserved for high-performance or aerospace use.

While these designations provide a convenient reference for relative strength, they are not universal across all manufacturers. Actual material properties—including tensile strength and modulus—should always be verified using the supplier’s Technical Data Sheet to ensure accurate performance data for a specific application.

Common Manufacturing processes

The following is a breakdown of common manufacturing methods used in the composites industry. Each method offers distinct advantages, and the selection of a process should be based on the specific requirements of a project, including part geometry, production volume, material performance, and cost considerations.

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Resin Infusion (Vacuum Infusion Process)

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Resin infusion involves placing dry fabric layers into a mold and sealing them under a vacuum bag. Once the air is evacuated, resin is drawn through the fabric stack via vacuum pressure, thoroughly wetting out the fibers before curing. This process produces a high fiber-to-resin ratio and a smooth surface finish while minimizing air entrapment and waste. It is commonly used for medium- to large-scale parts where consistent quality and reduced emissions are important. However, it requires careful setup and resin flow control to ensure complete saturation.

Prepreg Autoclave Curing

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Prepregs are fabrics pre-impregnated with a precisely measured amount of resin and hardener, stored under refrigeration to prevent premature curing. Components are laid up in a mold, vacuum-bagged, and cured under elevated temperature and pressure inside an autoclave. The combination of heat and pressure consolidates the laminate and eliminates voids, resulting in the highest-quality composite parts with superior strength-to-weight ratios. This process is the standard in aerospace and high-performance automotive applications, though it requires specialized equipment and has higher material and processing costs.

Prepreg Out-of-Autoclave (OOA) Curing

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Out-of-autoclave prepreg processing uses similar pre-impregnated materials but cures them under vacuum and elevated temperature in a conventional oven, rather than in an autoclave. Advances in resin chemistry allow OOA systems to achieve near-autoclave quality with lower capital investment and easier scalability. While not as void-free as autoclave composites, OOA processes offer excellent results for large structures and applications where reduced equipment cost or size constraints are critical.

Wet Layup

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In the wet layup process, dry fabric layers are placed into a mold and manually saturated with liquid resin using brushes or rollers. The laminate is then consolidated by hand or with vacuum bagging and allowed to cure at ambient or elevated temperature. Wet layup is the most accessible composite fabrication method, ideal for prototyping and low-volume production. However, it typically yields lower fiber volume fractions and less consistent mechanical properties compared to vacuum-assisted or prepreg methods due to variability in resin content and air entrapment.

Compression Molding

‍Compression molding involves placing a measured charge of composite material—often chopped fiber, sheet molding compound (SMC), or bulk molding compound (BMC)—into a heated matched-die mold. The mold is then closed under high pressure, forcing the material to flow and conform to the cavity shape. This process offers fast cycle times, excellent repeatability, and suitability for high-volume production of complex geometries. It is widely used in the automotive and consumer goods industries where structural efficiency and surface finish are both important

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