Carbon Fiber Sheet & Tube

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Carbon fiber or aluminum: which is better for tubes, frames and arms?

Carbon fiber wins when weight matters. A carbon fiber laminate weighs about 1.6 g/cm³ against 2.7 g/cm³ for aluminum[1], so the same part is roughly 40% lighter. Stiffness depends on the layup: woven carbon is about 20% less stiff than aluminum, while unidirectional carbon is about 1.8 times as stiff along the fiber[2][3].

~40%lighter than aluminum at the same volume
120 GPaunidirectional T300 laminate, along the fiber
55 GPawoven T300 laminate
~6×more thermal expansion in aluminum

How do the numbers compare?

Property Aluminum Woven carbon (T300, 3K) Unidirectional carbon (T300) Unidirectional carbon (T700)
Density (g/cm³) 2.7[1] about 1.6[1] about 1.6[1] about 1.6[1]
Tensile modulus (GPa) 68.9[1] 55[2] 120[3] 125[4]
Tensile strength (MPa) see alloy sheet 650[2] 1,900[3] 2,300[4]
Specific stiffness (modulus ÷ density) 25.5 34 75 78

Carbon values are laminate test results (ASTM D3039) from the technical data sheets of the prepregs we use, not fiber values[2][3][4]. Fiber strength is far higher, but a part is a laminate, so compare laminates.

What does that mean for a tube?

A roll-wrapped tube is usually mostly unidirectional plies with a woven outer ply for looks and crush resistance. That puts most of the fiber along the tube, where bending loads act, so a carbon tube can be both lighter and stiffer than an aluminum tube of the same size. An all-woven tube or plate is lighter but not stiffer.

Roll-wrapped carbon fiber round tubes
Roll-wrapped carbon tubes: unidirectional plies inside, a woven ply outside.
Road bicycle with a carbon frame
Bicycle frames were among the first mass-market aluminum parts replaced by carbon fiber.

Where does aluminum still win?

  • It bends before it breaks. Aluminum yields and dents. Carbon stays elastic until it fails, without warning. Design carbon parts with a margin and avoid sharp notches.
  • Point loads and clamping. Thin carbon walls can crush under a clamp or bolt. Use inserts, sleeves or a thicker wall at fixing points.
  • Cost. Aluminum extrusions are cheaper per part. Carbon pays off when weight, stiffness, fatigue or corrosion resistance earn it back.
  • Heat. Aluminum keeps its strength at temperatures where an epoxy laminate softens. See how hot carbon fiber parts can get.
  • Contact with metal. Carbon touching bare aluminum in wet conditions causes galvanic corrosion of the aluminum. See how to join carbon fiber to metal.
TipCarbon fiber barely expands with heat; aluminum expands about six times as much[1]. For measuring frames, optical rails and long gantries, that stability often matters more than the weight saving.

Which carbon option should I ask for?

Your priority Ask for
Lowest weight, visible finish 3K woven tube or sheet, glossy or matte
Highest bending stiffness Roll-wrapped tube with unidirectional plies, or a pultruded tube or rod
Stiffness at the lowest price Pultruded tube, rod or strip
Flat parts cut to shape Carbon sheet, CNC-cut from your drawing

Send the aluminum part’s size, the load and your target weight through the quote form. Standard sizes are on the carbon fiber tube and carbon fiber sheet pages.

Sources

  1. DragonPlate, “Carbon Fiber vs Aluminum”: aluminum 2.7 g/cm³ and 68.9 GPa, carbon fiber composite about 1.6 g/cm³; aluminum expands about six times as much as carbon fiber
  2. Technical data sheet, woven T300 prepreg T200R4024T: laminate 0° tensile strength 650 MPa, modulus 55 GPa (ASTM D3039)
  3. Technical data sheet, unidirectional T300 prepreg C200R2824T: laminate 0° tensile strength 1,900 MPa, modulus 120 GPa (ASTM D3039)
  4. Technical data sheet, unidirectional T700 prepreg C200Z3624S: laminate 0° tensile strength 2,300 MPa, modulus 125 GPa (ASTM D3039)

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