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Back to Basics: Carbon Fiber vs Fiberglass vs Kevlar/Aramid

Apr 28th 2021

While many of our readers and customers know their composite materials like the back of their hands, there are plenty of newcomers we speak to daily that are new to the composites world. Today we thought we’d get back to the basics and review the three primary fibers used in composites. Think of it like getting to reacquaint yourself with an old friend you know well but haven’t talked to in awhile.

Carbon Fiber is most highly known to be top choice in aerospace and industrial applications due to its high tensile strength, low density, high rigidity, and thermal conductivity. In fact, Carbon Fibers yield the highest material strengths across the board when compared to Kevlar or Fiberglass options. It exceeds comparable fibers in strength to weight and stiffness categorizes. For this reason, it replaces alloys in aerospace components that formerly used aluminum or titanium. Carbon Fiber composites excel at keeping dimensional tolerances as loading is applied. Although these properties are great to have, this also causes carbon fiber laminates to suddenly break or splinter suddenly upon maximum values being exceeded. Carbon Fiber does not absorb energy well, however, transfers that energy along its fibers to other sources. (Good or Bad dependent on application) It is best used with epoxy resins to achieve its maximum properties. Although special tooling and processes are not needed for fabrication purposes, vacuum equipment will greatly increase Carbon Fiber’s laminate quality.

Common Applications: High Performance Aircraft & Aerospace Structures, Drones, Skeletal Tubing, Spoilers, Boats, Sporting goods (rackets, clubs, bats, sticks, arrows, bikes) Stiffeners, Racing Parts, High End Automotive Panels, Electronics, Medical Imaging, Musical Equipment, Fishing Rods and Components

Advantages

What to watch for:

Highest Tensile / Compressive Strength
Highest Strength to Weight
Most Rigid
Low Coefficient of Thermal Expansion
High EMI Shielding Properties

High Cost
Corrosive to metals in contact with CFRP
Breaks suddenly
Electrically Conductive
Low Impact Strength


Fiberglass is the most used fabric type in composites today. Fiberglass’s low cost and overall strong physical properties make it a work horse for economically minded hobbyists and professionals alike. Fiberglass has a footprint in nearly every industry known to man. Fiberglass composites will still yield strong, light weight parts that can be used the widest variety of applications. There are 2 main types of fiberglass used in composites today.
Upon initial use of fiberglass, E-Glass was made for electrical purposes because it is non-conductive. This cheaper option is widely used in many applications today and while not limited to, is used as an interface for secondary bonding with carbon fiber parts to metal parts. 

S-Glass is signified by strengthened fiberglass. It has ~20% strength characteristics, is stiffer and more impact resistant. While carrying a higher cost compared to E-Glass, it may deliver better cost performance depending on the application or structural needs. 

Often, both types of glass are utilized in a structure. S-glass is known to be an excellent for the outer layers of a structure as it provides rigidity and strength to a structure. E-glass then reinforces and provides energy absorption to the composite. Fiberglass can be used with all thermoset resin applications. (Polyester/Vinylester/Epoxy)

Common Applications: Boats, Insulation, Auto Parts, Pools, Waterslides, Piping, Cooling Towers, Slip Resistant Surfacing, Aerospace, Fishing Rods, Pressure Vessels

Advantages

What to watch for:

Best Cost Performance
High Tensile Strength
High Energy Absorption
High Availability in differing patterns
Widely Used, High Knowledge Base
Chemically & Moisture Resistant
Widest Variety of Resin Types
Electrically Insulative

Lowest Strength to Weight Ratio
Comparably Lower Strengths than CF
Less Rigid than CF and Kevlar


Kevlar is the lightest weight and toughest fabric type widely used in composite industry. Being used today as a fabric alone in bullet proof vests, impact and cut resistant safety equipment, and used as a fire retardant. Kevlar has the highest benefit between being used as fabric or composite. In composite form, Kevlar is used to produce structures that provide the best impact and abrasion resistance characteristics in comparison to other fibers. Kevlar fills the gap of stiffness between fiberglass and carbon fiber Kevlar fibers will provide high strength reinforcement Kevlar can be difficult to cut and process unless the correct tools are used. Kevlar composite parts are almost always painted as Kevlar composites will degrade over time when exposed to UV radiation and sunlight.

Common Applications: High Performance Aircraft & Aerospace Structures, Body Armor, Surf boards, Motor Sports Protection, Kayaks, Canoes, and Pressure vessels, Boat Hull Transoms, Automotive body parts

Advantages

What to watch for:

Lightest Weight / Density
Highest Toughness
Highest Energy Absorption (+Vibration)
Highest Impact Resistance
Highest Crack Resistant
High Strength to Weight ratio
Chemically Resistant
High Level of Workability

Low Compressive Strengths
Fibers Absorb Water (~3.5%)
High Cost
Toughest challenge to process / cut / prep
Poor UV Resistance

All composite fibers have clear advantages and disadvantages. Even with the information above, selection of a component’s fiber can still be tricky. However, there is nothing to say that a component or structure cannot have the best of all materials. 

Taking a kayak for example, using Kevlar as the material will yield a light weight, energy absorbent kayak. However, it may not be very durable once it crashes upon a rock resulting in compression damage. Use of S-Glass fiberglass layer on the outside reinforced with a layer of glass can make a huge difference in the lifespan of the kayak. Using the lightweight advantage of Kevlar in the inner layers may produce the best kayak ever seen. A carbon fiber kayak alone will provide weight savings as the strength to weight ratio is the best and provides a means to engineer a highly rigid and strong hull. The kayak will end up very costly and still may not provide the impact and fatigue resistance needed for a long life. Hybrid materials using CF / FG and Kevlar/CF are also made. Using a Kevlar/CF hybrid could yield a lightweight kayak that takes advantage of both he materials strengths, being stiff while still being able to absorb energy.

The overall beauty of composites is that there can be a thousand different ways to achieve a goal. Composites provide the world an opportunity to use creativity to solve problems using an endless array of weaves, fibers, yarns, twills, and resins.

Characterization

Carbon Fiber

Kevlar

Fiberglass

Cost

1

3

10

Tensile Strength

10

8

7

Strength to Weight

10

9

5

Compressive Strength

10

3

6

Rigidity

10

6

6

Fatigue Resistance

6

10

8

Abrasion Resistance

7

10

7

Processing

7

6

10

Conductive

Yes

No

No

Corrosive to Metals

Yes

No

No

Heat Resistance

10

10

10

Moisture Resistant

10

5

10

Chemical Resistance

10

7

10

UV Resistance

Yes

No

Yes