Thermal insulation: What is it and how is it used?

Thermal insulation refers to the many ways to inhibit the transfer of heat from one object to another. This may refer to the heat from a boiler escaping through the chamber walls into the surrounding atmosphere, the hot and cold faces of processing equipment in industrial facilities or the high ambient temperatures of processing lines, which can impact the sensitive electronics of automated devices.

Working principles of thermal insulation

It is worth reviewing some of the basic concepts of thermal conduction and insulation. Heat is a thermodynamic quantity of thermal energy that flows from one system to another when there is a temperature differential between the two. It is transferred via one of three different methods:

• Conduction
• Convection
• Radiation

Thermal insulation is typically used to limit heat transfer via conduction, which requires objects to be in direct contact with one another. Some types of insulation utilize reflective coatings to prevent heat transfer via radiation, but this article mainly deals with heat transfer between contacting objects.

The rate at which heat transfers between objects is determined by the thermal conductivity (k) of materials. Metals and ceramics with high thermal conductivities are often used for heat transfer applications. Silicon carbide, for example, with a nominal conductivity of 170 W/m-K, is routinely used to engineer high-temperature heating elements for industrial ovens and furnaces.

Vice versa, low thermal conductivities yield extremely high resistance values. Many silica-based materials boast resistance values of less than 2 W/m-K, which can effectively mitigate the absorption of heat to minimize transfer. Though the thermal conductivity of insulation materials is a critical factor in performance, many other properties must be considered, including:

• Density
• Specific heat capacity
• Thickness
• Thermal bridging

What materials are used for thermal insulation?

The widespread historical use of asbestos in such formats highlighted the potential dangers inherent in certain materials. Despite an outstanding resistance value of 0.08 W/m-K, asbestos has known carcinogenic effects and is associated with a wide range of serious long-term health conditions.

In the 1970s, fiberglass insulating materials were introduced to replace asbestos and to ensure safe and optimal performance in any application area. Fiberglass emerged as the most-widely used fiber, however other fibers such as Kevlar and Nomex can be used for applications with a lower continuous operating temperature. Silica and ceramic fiber can be used for applications with a continuous operating temperature over 1,800° F/982° C.

The key benefits of fiberglass thermal insulation

The specialty configurations of fiberglass thermal insulation are designed to satisfy high thermal demands alongside additional performance parameters, such as conforming to complex geometries or adhering to surfaces. Fiberglass rope, tape, cloth and sleeving insulation is made with high-quality fiberglass that has been specifically manufactured to provide exceptional properties:

Chemical resistant

Fiberglass textiles insulation offers excellent resistance against a wide range of chemicals. Therefore, it is suitable for many applications in harsh environments, such as chemical processing, and the gas and oil industries. The fiberglass protects against chemical damage, increasing the equipment’s lifespan.

Durable

The durability of fiberglass insulation is outstanding, enabling it to last for years, even in the harshest environments. Because it is resistant to chemicals, environmental factors, and high temperatures, it can be used in indoor and outdoor applications without breaking, cracking, or compressing.

Easy installation

Fiberglass textiles insulation can be installed easily and quickly, which makes it a cost-effective insulation solution for applications of any size and in any environment. It can be configured in different ways, such as knit or woven and can be cut to size to meet specific requirements.

Energy efficient

As an insulation material, fiberglass textiles provide excellent thermal properties that help keep heat inside equipment and systems. As a result, fiberglass rope helps to reduce energy consumption and increases energy efficiency, which lowers energy bills.

Fire resistant

Another reason for using fiberglass rope as an insulation material is that it is highly fire-resistant. This is an ideal solution in environments requiring high levels of fire safety as it helps slow down the spread of flames, which helps minimize damage to objects and personnel.

High-temperature resistant

Without its high-temperature resistance, fiberglass rope would not be an effective insulating material. It can withstand extreme temperatures (1,000° F / 538° C) and will not burn or smolder.

Strength

Fiberglass rope maintains outstanding dielectric and high tensile strength even under extreme temperatures and pressures. The strength properties are due to the E-glass it is manufactured with, making it an easy choice for insulating applications.

In certain applications, additional processing such as adding a coating can enhance the properties of the textiles. For example, fiberglass yarn can be converted into a tightly woven textile rope or tape, and then coated with a mineral or silicone coating to increase the thermal or abrasion resistant properties. Each configuration benefits from the underlying thermodynamic stability of fiberglass that suits a broad range of applications, while in a configuration that best suits the application requirements.

What are the standard configurations of fiberglass thermal insulation?

Naturally, materials with high heat resistance values are formatted in the most dense and thick formats possible to provide effective thermal insulation. Products based on fibrous and needled mats are among the most popular configurations as they can be fabricated into products that are installed quickly and efficiently, such as removable insulation blankets. However, flexible formats also provide a much-needed measure of versatility when it comes to wrapping thermal insulation around complex mechanisms, filling tight voids or insulating wires.

Fiberglass thermal insulation can be manufactured as ropes, tapes, cloths or sleeving to address applications where a fiberglass blanket or mat may not be suitable. Typically, these configurations are either knit, braided or woven and can be engineered in varying thicknesses, widths and densities.

Braided and knit thermal insulation ropes

Fiberglass ropes made with E-glass fiberglass yarn offer a combination of strength, durability and corrosion resistance. They can be braided or knitted into different configurations that have exceptional mechanical and thermal properties, and with a continuous use limit of 1,000° F/538° C. The flexibility of fiberglass allows for customization to meet specific application requirements. As an example, fiberglass can be braided over a dense silicone core in round, rectangular and square configurations for sealing in applications with high compressibility.

Figure 1: Fiberglass thermal insulation rope. Source: Mid-Mountain Materials

Woven and knit thermal insulation tapes

Fiberglass tapes can be woven or knit depending on the density required, and coated with various coatings such as vermiculite, graphite, silicone or mineral coatings. When coated, these tapes are excellent for use in working environments such as metalworks and pipe wrapping.

Bolt hole tape is a more custom tape that slips over bolts given the loose weave in the center and has abrasion resistant properties when coated with silicone.

Figure 2: Bolt hole tape: uncoated and coated with silicone rubber. Source: Mid-Mountain Materials

Woven tadpole tape is engineered to custom specifications and has a continuous woven fiberglass bulb and tail. This tried-and-tested bulb-shaped format is widely used as door, furnace and oven seals and act as chemical and thermal barriers in gas fireplaces. This tape is often coated with various coatings and has PSA applied to the tail for adhesion to a glass or metal frame.

Figure 3: Woven tadpole tape: coated and uncoated. Source: Mid-Mountain Materials

Thermal insulation cloth

Fiberglass cloth has long been used for thermal insulation. Plain fiberglass cloth, aluminized fiberglass cloth or coated fiberglass cloth are so versatile as insulation as they can be used in their full width, slit into narrow widths or fabricated into custom components such as welding blankets, engine seals and insulation blankets and jackets. Adding aluminum foil or a coating (silicone, mineral) enhances the properties of the fiberglass and is beneficial in applications where increased abrasion or chemical resistance is required.

Figure 4: Silicone coated fiberglass fabric. Source: Mid-Mountain Materials

Thermal insulation sleeving

Braided or knit sleeving is often used as electrical insulation as cable insulation sleeves, but is also useful for satellite harnesses, robot protection solutions, and other applications that require a custom fit in spaces that may be too small for a rope or tape. In addition to fiberglass, other fibers such as silica, Kevlar, Nomex and carbon, or a hybrid of fibers, can be used for insulative applications.

Figure 5: Thermal insulation sleeving: carbon (far left) and hybrid fibers. Source: Mid-Mountain Materials

Mid-Mountain Materials, Inc., is an ISO 9001:2015 certified manufacturer of engineered thermal insulation products located in Seattle, Washington. We develop thermal insulation barriers and seals for emissions control, environmental protection and other applications in varying sectors including aerospace, aluminum, automotive, petrochemical, robotics and welding.

Their HYTEX® 1000 Fiberglass Textiles offer thermal insulation protection up to 1,000° F/538° C. Please visit the Mid-Mountain Materials website to learn more about their products.

Kevlar and Nomex are registered trademarks of the E.I. DuPont Company, Wilmington, Delaware.