There are a number of reinforcing fibers available, the most common used are glass and carbon fibers. These fibers are aligned either in unidirectional (UD) or crosswise orientation to the composite being produced.  

The mechanical properties of the composite are largely determined by the reinforcement chosen, the orientation of those fibers, and the total content of fiber used (in relation to the matrix) 

Reinforcing fibers can be in the form of a roving or tow (a single continuous strand of fibers), in mats, and in unidirectional or multiaxial fabrics.  

Carbon or graphite fibers

Today carbon fiber is widely used to help reduce weight while maintaining strength and stiffness requirements.  

Exel uses a range of carbon fibers in our manufacturing. These include high strength (HS), high modulus (HM), PAN type carbon fibers, and ultra-high modulus (UHM) pitch type carbon fibers. 

Our carbon fiber products typically offer the following advantages:  

  • Light (80 % lighter than steel and 45 % lighter than aluminum) 
  • Extremely strong (UTS up to 3000 Mpa), high specific strength 
  • Extremely stiff (E from 80-400+ Gpa), high specific stiffness 
  • Very low coefficient of thermal expansion 
  • Low maintenance 
  • Weatherproof 
  • Low water absorption 
  • Good fatigue and creep properties 
  • High vibration damping 

For example, our pultruded carbon fiber profiles are much stronger than steel, lighter than aluminum and may be stiffer than steel (stiffness range 100-400+ GPa). 

Typical properties of carbon fibers: 

Type Density Tensile strength Tensile modulus 
  [kg/dm3] [Gpa] [Gpa] 
HS1 1.75 3.31 228 
HS2 1.80 5.0 248 
IM 1.74 4.50 296 
HM1 1.81 2.41 393 
HM2 1.96 1.52 483 
UHM 2.15 2.24 724 

Glass fibers

Glass fiberare the most widely used reinforcement material in the pultrusion and pull-winding industry. Glass fiber is used as a reinforcing agent for many polymer products; the resulting composite material, properly known as fiber-reinforced polymer (FRP) or glass-reinforced plastic (GRP), is commonly called “fiberglass” in popular usage. Glass fiber is formed when thin strands of silica-based or other formulation glass are extruded into many fibers with small diameters suitable for textile processing. 

Glass fiber has good tensile, compression and impact properties. We consider fiberglass to be a high-performance material.  

  Specific gravity Tensile strength Tensile modulus Coefficient of thermal expansion 
    [Mpa] [Gpa] 10-6/K 
E-glass 2.58 3 450 72.5 5.0 
ECR-glass 2.62 3 625 72.5 5.0 
S-glass 2.48 4 590 86.0 5.6 


Typical properties of fiberglass (GRP) profiles and tubes are 

  • Light weight (75 % lighter than steel, and 30 % lighter than aluminum) 
  • Very good specific strength 
  • Very good specific stiffness 
  • Low coefficient of thermal expansion 
  • Thermal insulation 
  • Non-magnetic 
  • Good chemical resistance 
  • Low maintenance 
  • Weatherproof 
  • Low water absorption (high fiber content) 
  • Cost effective 

Exel is using glass fibers in different forms: 

  • Roving 
  • Woven roving 
  • Mats 
  • In combinations of rovings, mats and woven rovings. 

Aramid fibers

Aramid fibers have low density (1.45 kg/dm3) and high tensile strength. Aramid fibers have very good impact strength properties and they are used in anti-ballistic applications. This table compares properties of pultruded aramid, glass, and carbon profiles.  

Fibre Unit Carbon Glass Aramid 
Density [kg/dm3] 1.5-1.6 1.9-2.0 1.3 
Tensile Modulus [Gpa] 80-400+ 38-45 70-75 
Tensile strength [Mpa] 1500-3000+ 800-1200 800-1500