Thermal Conductivity Resources

Top 10 Thermally Resistive Materials and Gases

Introduction

Thermal resistance is the inverse of thermal conductivity and determines a materials insulative properties. It can be described as a materials ability to resist the flow of heat through it. For gaseous substances, thermal resistance is mainly a factor of ineffective heat transfer and low thermal conductivity. Thermal resistance in solid is a function of the materials thickness combined with low conductivity and can be represented by an R-value. R-values are extremely useful for the construction of buildings or homes to determine the quantity and type of insulation needed to restrict heat loss. The values expressed in this paper represent the thermal conductivity of a gas or solid measured in Watts per minute per degrees Kelvin W/m•K. Due to thermal resistance being the opposite of thermal conductivity, these values are noticeably small.

1. Carbon Dioxide CO2: 0.015 W/m•K

Carbon Dioxide is a colourless, odorless, non-toxic gas that is formed from covalent double bonds occurring between a carbon atom and two oxygen atoms. This molecule is a major component in the carbon cycle that enables plant growth and assist in photosynthesis. Carbon dioxide is the most abundant greenhouse gas in the atmosphere and its levels continue to grow exponentially due to the increased burning of fossil fuels. Greenhouse gases are molecules that absorb infrared radiation and contribute to the warming of earth’s surface temperature. CO2 levels in the atmosphere today are higher than ever before in earth’s history. In 2017, levels reached 405ppm (parts per million) and are expected to reach 900ppm by the end of the 21st century. Due to the extreme warming impact CO2 has on the environment, one of the largest climate change goals for countries across the globe is to substantially lower their carbon dioxide emissions over the next decade. If levels continue to increase at this alarming rate the impacts will be devastating to millions of species and ecosystems potentially damaging them beyond repair.

2. Ethylene C2H4: 0.017 W/m•K

Nitrogen is the most abundant gas in the atmosphere contributing to 78% of the air’s composition. Nitrogen is a colourless, odorless gas that is frequently used in food processing and to preserve perishables, often in the form of liquid nitrogen. It is also very important element for plant growth and other biological processes. When nitrogen is fixed it bonds with hydrogen to produce ammonia (NH3). This is the form of nitrogen that can be absorbed by plants. Nitrogen fixing can be performed synthetically by preforming the Haber Process or naturally by nitrogen fixing bacteria that are present in soil. Every year the Haber Process alone produces 150 million tons of ammonia that can be used to promote crop and ecosystem growth.

3. Oxygen O2: 0.024 W/m•K

Oxygen is the second most abundant gas in atmosphere contributing to 21% of air’s composition. Oxygen is crucial to animals that use it to preform cellular respiration (breathing). It is one of the most versatile gases and can create a bond with almost any other element. Pure oxygen is used in breathing tanks for scuba diving as well as for medical applications. Steel production is the largest industrial consumer of oxygen and uses as a filtering agent to remove any undesired compounds from a steel mixture. The high thermal conductivity of O2 enables it to be used as coolant in computers to decrease their internal temperature and prevent the overheating of rigs.

4. Water Vapor H2O: 0.024 W/m•K

Water Vapor is the gaseous form of water and is considered to be the most important greenhouse gas contributing to 90% of the warming on earth’s surface. Heat radiated from earth’s surface is absorbed by water molecules present in the atmosphere before it can escape to space. This process creates the second largest warming mechanism next to the radiation from the sun. The presence of water vapor in the atmosphere and hydrosphere has allowed for life to be supported on our planet that would not be able to survive otherwise.

5. Air: 0.024 W/m•K

Air is a uniform mixture of gases made up of 78% nitrogen, 21% oxygen and 1% other (mainly argon and carbon dioxide). Most of the elements present in air have extremely low thermal conductivities which contribute to the mixture’s insulative properties. Air’s composition can vary depending on location and altitude. Air at a higher altitude can hold almost double the amount of water vapor which can lead to a minor decrease in thermal resistance.

6. Urethane (polyethene) Foam Insulation: 0.026 W/m•K

Urethane foam is one insulation materials with the highest thermal resistance leading to its popular use in the construction of homes. It can be manufactured as a spray or in boards. Urethane insulation can adhere to all surfaces including steel, concrete or wool and serves as an excellent vapor/air barrier. In Quebec alone, 41 million tons of recycled plastic bottles are used annually to produce urethane insulation. This extremely efficient and sustainable insulation is ideal for protecting a home against heat and energy loss.

7. Rock (mineral) Wool Insulation: 0.034 W/m•K

Rock wool insulation is composed of basalt and recycled slag (byproduct from steel production) and generally comes in batts. It is formed by heating natural rock to 3000°F until it has melted to a magma consistency. The magma like substance is then spun into dense fibers and pressed into large batts. Rock wool has a higher R-value than fiberglass, the leading insulation in the North American market. It is very sustainable being composed of over 70% recycled material. Rock wool is hydrophobic (moisture repellant) and fire resistant so it can easily be used as a fire stop in homes.

8. Fiberglass: 0.042 W/m•K

Fiberglass has been the leading insulation in North America for over 80 years due to its affordability, simplicity and effectiveness. It is made of glass fibers woven together and then compressed into long rolls or batts. Fiberglass contains 20-30% recycled materials which is substantially less than its biggest competitor rock wool. Although the less sustainable insulation option, it does come in a wider array of sizes and is also available in loose fill.

9. Cork: 0.043 W/m•K

Cork has an extremely unique honey comb cellular structure that contributes to its success as an insulator. Each cork cell is a 14-sided polyhedron that has a hollow inside filled with air. The cell membranes create a waterproof and airtight barrier making each cell very flexible. The air pockets present inside each cell increase the material’s thermal resistance and lower its density. Cork in its natural form is also a very good fire repellant and sound/vibration barrier.

10. Calcium Silicate Ca2SiO4: 0.046 W/m•K

Calcium silicate is a mixture of calcium and silicon atoms that create a fine white powder when combined. It is often used in building materials such as glass, cement, bricks and tiles for roofs. The high thermal resistance of calcium silicate enables it to be used as insulation in pipes and conductors to restrict heat and energy loss. A non-thermal use of calcium silicate is in baking and food ingredients. It acts as an anticaking agent because it is very efficient at absorbing moisture and water.

References

Carbon dioxide. (n.d.). Retrieved from https://www.sciencedaily.com/terms/carbon_dioxide.htm Climate Change: Atmospheric Carbon Dioxide: NOAA Climate.gov. (2018, August 01). Retrieved from https://www.climate.gov/news-features/understanding-climate/climate-change-atmospheric-carbon-dioxide Contributor. (2017, March 24). What’s the Difference: Fiberglass vs. Mineral Wool Insulation. Retrieved from https://www.thehousedesigners.com/blog/whats-difference-fiberglass-vs-mineral-wool-insulation/ Ethylene – Thermophysical Properties. (n.d.). Retrieved from https://www.engineeringtoolbox.com/ethylene-ethene-C2H4-properties-d_2104.html Imf. (n.d.). Urethane – Polyurethane Foam: Isolation Majeau. Retrieved from https://www.isolationmf.com/en/insulation-urethane.html Johnson, D. (2019, March 02). 10 Uses for Oxygen. Retrieved from https://sciencing.com/10-uses-oxygen-8634456.html Summary. (n.d.). Retrieved from https://neutrium.net/heat_transfer/thermal-conductivity-of-common-materials/ Water Vapor. (n.d.). Retrieved from https://earthobservatory.nasa.gov/global-maps/MYDAL2_M_SKY_WV Products – CorkLink – cork products direct from Portugal. (n.d.). Retrieved from https://www.corklink.com/index.php/products/ Calcium Silicate: Baking Ingredients. (n.d.). Retrieved from https://bakerpedia.com/ingredients/calcium-silicate/ Author: Kallista Wilson, Junior Technical Writer at Thermtest