Exploring the Thermal Conductivity of G10 in Engineered Composite Materials

Published on June 21, 2024

A laminated thermoset composite that consists of a matrix made from epoxy resin and woven glass cloth was first introduced in the 1950s. This material became the first epoxy laminated glass for printed circuit boards, known by its brand name Garolite or G-10. Thermal conductivity of the composite was one reason for its use in this regard, while other properties make it an ideal material for this and numerous other applications. G-10’s thermal conductivity also presents other useful characteristics, such as chemical resistance, dielectric properties, and good tensile strength.

These qualities make it incredibly versatile, though a few composites use the material that is sometimes referred to as G-10. Thermal conductivity properties are enhanced by the flame-retardant version of G-10, designated sometimes as G-10FR, though more often referred to as FR-4. These characteristics are also present in the cryogenic composite made from G-10. The thermal conductivity properties of G-10CR make it an ideal material for use under extremely cold conditions when hydrogen, nitrogen, oxygen, and other gases turn into liquids. A proper understanding of G-10’s thermal conductivity and other properties can determine whether it’s the best material for a specific application.

G10 Thermal Conductivity in Composites

Fabrication involves stacking multiple layers of glass cloth and then soaking them in epoxy resin, after which the material is compressed with heat until cured to make the composite known as G-10. Thermal conductivity and other desirable properties can be augmented through additions to the composite fabricated in sheets that are only a few millimeters thick. Because of its initial use as a substrate for printed circuit boards, the National Electrical Manufacturers Association’s designation of Garolite as G-10 has stuck.

Though similar to Micarta and laminates made with carbon fiber, glass cloth is used as a filler rather than a matrix when making G-10. Thermal conductivity, tensile strength, dielectric, and other properties make G-10 one of the toughest glass fiber laminates on the market. Because of its toughness, G-10 is favored over many other materials. It’s one of the most commonly used types of laminate. Additionally, its low moisture absorption and chemical resistance make it ideal for use in harsh marine environments and when exposed to other environments containing excessive moisture or humidity.  

G10 Thermal Conductivity & Other Properties

Once fabricated, G-10 is incredibly stable over a wide range of temperatures while possessing a good strength-to-weight ratio and a low moisture absorption rate. Additionally, two special types of G-10 – FR-4 and G-10CR – are fire resistant and can handle cryogenic temperatures, respectively. When looking at the characteristics of G-10, thermal conductivity and resistance to thermal shock make it suitable for use under conditions where extreme temperatures occur.

Some noteworthy properties of G-10 include: 

  • Bond strength of 154.8 kg per cm² (about 2200 psi)
  • Compressive strength of 2812 kg per cm² (about 40,000 psi)
  • Flexural strength lengthwise equivalent to 5273 kg per cm² (about 75,000 psi)
  • Impact strength according to Izod testing of 14.00 lengthwise at 49°C
  • Maximum temperature of 140°C (284°F)
  • Relative density of 1.8 in comparison to water
  • Rockwell hardness rating of 110 on the M scale
  • Self-extinguishing with a UL 94 HB (horizontal burn) flammability rating
  • Shear strength of 1335.8 kg per cm² (about 19,000 psi)
  • Tensile strength of 4570 kg per cm² (about 65,000 psi)
  • Water absorption rate of .11 of a percent over 24 hours

In addition to these properties, G-10 also has a relatively low shearing strength, which allows for higher throughputs and quicker fabrication.

G-10, G-10CR & FR-4

When considering G-10 thermal conductivity, two composites derived from the material need to be considered: FR-4 and G-10CR. FR-4 is also sometimes referred to as G-10FR, and though the two composites are similar, one can’t be substituted for the other in every application. FR-4 refers to the material’s augmented fire-resistant or fire-retardant properties, so often, FR-4 can be used in place of G-10. The thermal conductivity of the two materials is similar, but for applications that require fire resistance, G-10 shouldn’t be used.

G-10 is also often used to describe G-10CR, which can withstand subzero conditions. Its functions in support of cryogenic applications enable the storage of samples frozen at subzero temperatures, which requires a special type of G-10. Thermal conductivity properties offered by G-10CR allow for producing cryogenic neck tubes used in Dewars containers. Since the composite is relatively inexpensive and fairly strong, G-10 is often used to replace stainless steel in cryogenic applications.

Downsides of G-10

Depending on where it’s used, parts made from G-10 can last incredibly long. Those within a machine’s interior will likely last longer than the equipment. However, exposure to sunlight will shorten the lifespan of G-10. Thermal conductivity, dielectric properties, and other characteristics make composites useful in many situations, though products made using G-10 can’t be made via injection molding but must rather be machined.

Dust from machining glass and epoxy is known to be a factor in respiratory illnesses and may present a risk for lung cancer. Therefore, workers machining G-10 must wear respirators or sufficiently protective masks to ensure their workstation is properly ventilated. This means that care should be taken when machining materials made from G-10. Thermal conductivity and other properties the composite provides must be balanced against the costs of mitigating the material’s hazards.

Additionally, epoxy resins are generally combustible, actively burning once alight, which in turn causes them to emit toxic gases. For this reason, the FR-4 composite has largely replaced G-10 in applications where fire is a threat, with an ability to withstand heat up to 140°C (284° F). However, despite these downsides, G-10’s properties make it an incredibly useful composite used in many industries for multiple applications.

G-10 Applications & Industries 

As a high-performance reinforced glass polymer, G-10 is often used for applications requiring a certain degree of chemical resistance, including water and oil. For this reason, G-10 is often used for industrial and marine applications. Its low moisture absorbency also makes it a good choice for components for boats and other sea-going vessels. Due to its dielectric properties, parts made from G-10 are often used for ship engines. Additionally, due to its water-resistant properties, it’s often used for patching boats.

The ability to insulate against electricity also means printed circuit boards can still benefit from using G-10. Thermal conductivity properties combined with flame retardance and extremely low coefficient of thermal expansion also make it desirable for the medical device, marine, and aerospace sectors. Generally, however, G-10 works best when it’s not exposed to ultraviolet radiation, as too much sunlight causes it to degrade and lessens certain properties.

Applications for G-10 include: 

  • Boating applications
  • Cryogenic equipment like neck tubes
  • Diagnostic equipment for healthcare industry
  • Electrical insulators
  • Electrical test boards
  • Gears, guides, pulleys, rollers, and other components  
  • Handles or grips for firearms, knives, and other weapons or tools
  • Printed circuit boards
  • Rocket casings
  • Tooling for CNC machines like fixtures and jigs

Generally, G-10 comes in rods, sheets, and tubes. The composite is available in a wide range of colors to be incorporated into a product for aesthetics and its many useful qualities. Due to G-10’s exceptional mechanical and electrical properties, it’s also a key composite used in all types of electronics and robotics, and it is favored by mechanical engineers for internal components.

Engineered Composites from Spaulding 

Spaulding Composites, Inc. supplies specialty composites and fabricated products from these materials. As a company, Spaulding has been in business for over a century and a half, developing innovative materials for all industrial applications. This includes products made from G-10, such as cryogenic neck tubes for Dewars containers. To learn more about Spaulding’s products and services, we invite you to contact one of our customer service representatives today.