Carbon and fiberglass are both used to create high performance composite products, but each material has unique properties and benefits. When choosing a composite rod or tube for your application, Goodwinds Composites can help you decide between fiberglass and carbon fiber. We have years of experience working with both materials and our customers in a variety of industries, including aerospace, industrial equipment and manufacturing, musical instruments, sporting goods, marine, and many more. 

Carbon Fiber Composite Rods and Tubes 

Carbon fiber is a tiny (5 to 10 micrometers in diameter) strand of carbon atoms bonded linearly (each atom lined up in the same direction) via a process called polyacrylonitrile. The resulting carbon fibers are anisotropic, meaning their properties are directionally dependent; their strength depends on the carbon fiber’s orientation.

In pultruded carbon fiber rods and tubes, each carbon fiber is oriented in the same direction as the others and then pulled through a resin bath and cured through heated dies in a continuous process. These pultruded carbon fiber rods and tubes are extremely, linearly strong.  

Carbon fibers can also be turned into unidirectional (all fibers oriented in the same direction) fabric or woven (usually twill) fabric and pre-impregnated with resin. Carbon pre-preg fabric is used to manufacture roll-wrapped carbon tubes and molded parts. The carbon fabric can be layered so that each ply is oriented in a specific relation to the other layers to imbue specific attributes to the final tube, such as hoop strength or flexural strength. 

Strength and Stiffness

Carbon fiber is strong and stiff, as measured by its stiffness (called a modulus of elasticity or Young’s Modulus) and its tensile strength. Commercial carbon fiber used in the pultrusion process has a modulus of approximately 250 gigapascals (GPa). Carbon fibers possess a high tensile strength, ranging from 3 to 7 GPa.  

The modulus elasticity of steel is between 190 and 215 GPa, while the modulus of elasticity of aluminum is 69 GPa. Structural steel has a tensile strength of 0.4 – 0.7 GPa and aluminum has a tensile strength of 0.09 GPa. While steel is about as stiff as carbon, it has a much lower tensile strength. Carbon is also much less dense than steel or aluminum, making it much lighter weight for a given strength and stiffness. 

Density

Carbon composites, depending on the resin used and the fiber volume fraction, have a density of around 1.15g/cm3 to 2.25 g/cm3. Compare that to the density of steel at 7.8 g/cm3, 2.7 g/cm3 for aluminum, and 4.5 g/cm3 for titanium, and you can begin to see why carbon composites are considered lightweight.  

The density of carbon fiber composites can make them more difficult to machine than metals. They are “softer” when milled or turned and do not have the benefit of weight to keep them centered in machines. At Goodwinds Composites, we are experts in tight tolerance composites machining. 

Fatigue Resistance

Fatigue of a material is the progressive damage when that material is subjected to cyclic loads. In other words, how often and how much can a carbon fiber rod or tube be deformed and bounce back before it is damaged (breaks or delaminates or no longer rebounds)? Carbon fibers, because of their high stiffness and strength, can endure high, repeated loads or stresses. This fatigue resistance can be enhanced with resin choice and layup (in the case of wrapped composites) design, including ply orientation. The fatigue resistance of a specific carbon fiber rod or tube will depend on the repeated stresses placed upon it. 

Corrosion resistance 

Carbon fibers themselves are inert to environmental degradation, but the resin matrix of the composite can be broken down over time by UV light. Carbon composites do not rust or corrode in harsh environments, making them ideal for use in chemical processing, in highly acidic or basic environments, aquatic applications, or in-ground uses. 

Temperature Resistance 

The glass transition temperature of carbon fiber is 250 degrees Celsius. The temperature resistance of the carbon composite rod or tube depends on the resin used to make the composite. Goodwinds Composites pultruded carbon rods and tubes have a glass transition temperature of 100 degrees Celsius. 

Fiberglass Composite Rods and Tubes 

Fiberglass is made by combining silica sand with other inorganic materials such as soda ash, feldspar, and limestone in a furnace at 1371 degrees Celsius (2500 F) to create molten glass. This molten glass is then pulled into fibers or filaments between 5 and 25 micrometers in diameter (slightly larger than carbon fibers). These fibers are then combined with resin to create Glassfiber-Reinforced Plastic (GFRP), or fiberglass composites. Goodwinds Composites fiberglass rods are made via pultrusion and our fiberglass tubes are made using filament winding. Pultruded fiberglass rods align the filaments of glass along the length of the rod, making the rod extremely strong longitudinally. Filament-wound epoxy tubes feature glass fibers wound in a spiral pattern around a mandrel and then cured.  

Flexibility and Strength 

Fiberglass used in Goodwinds Composites’ rods and tubes (E-Glass) has a modulus of elasticity of 72 to 85 GPa, quite a bit lower than that of carbon fiber, meaning that fiberglass is much less stiff than carbon fiber. That is, for the same diameter rod, fiberglass is much more flexible than carbon fiber. The tensile strength of E-Glass is approximately 3.4 GPa, slightly less than standard carbon fiber but still much higher than steel or aluminum.  

Density

The density of E-Glass fiberglass is 2.54 to 2.6 g/cm3, higher than carbon fiber but still lower than steel, aluminum, or titanium. Comparing a fiberglass rod to the same diameter carbon rod, the fiberglass rod will be heavier. 

Corrosion Resistance 

Fiberglass composites are resistant to most acids, bases, oxidizing agents, metal salts, reducing gases, and sulfer gases. Fiberglass composites are insulators, meaning they are electrically non-conductive and are resistant to galvanic corrosion.  

Temperature Resistance 

Our fiberglass composite rods have a glass transition temperature of 77 degrees Celsius and our filament-wound epoxy tubes have a glass transition temperature of 99 degrees Celsius. 

Cost

Manufacturing fiberglass is less expensive than manufacturing carbon fiber. The differences in the materials aside, fiberglass is much less expensive than carbon.