Thermal Conductivity Insulators

The thermal conductivity of insulation materials is a measure for how easily heat can pass through them. It is one of the most important factors in determining R and U values.

Thermal Conductivity insulators are low thermally conductive and prevent heat transfer by conduction, radiation and condensation. This is how they keep heat in and reduce energy losses.

Wood

Wood is a material that is ideal for construction due to its natural insulating properties. It has a lower thermal conductivity compared to concrete, steel-frame construction or masonry construction. This reduces energy costs.

Wood is an excellent acoustic insulator. It reflects and absorbs sound waves, particularly when used in special structures that have porous insulation boards or empty spaces.

The thermal insulation properties are dependent on the moisture content in wood. When wood is dry, it is a good insulator. However, when it is wet it becomes a poor insulator.

Conduction, radiation, and convection are the three mechanisms that determine how fast heat moves into or out of a building. The thermal conduction of a substance is the rate at which heat moves in or out of a construction. This is measured as W/mK.

Cellulose

Cellulose foam insulation is a spray-on or loose-fill product that can be used for retrofitting walls and to fill open wall cavities. It is made from recycled newspapers and cardboard. Often, it is treated with a fire retardant.

The cellulose molecule, the most abundant biopolymer found on Earth, is used to make the fibers of plant tissues and exoskeletons (a grouping of filter-feeding organisms with tusks that live in marine environments). It has a linear chain structure. The cellulose molecule hydrogen bonds with other cellulose atoms to form elementary fibers.

It can be used as a thickener and emulsifier in food products. In image (a), an enlarged view of the microscopic cellulose structure reveals the fibrous and agglomerated nature of the paper, along with the elongated strands that contribute towards its thermal insulating qualities.

Minerals

Mineral wool is an insulating material made from spun fibers of melted, fluffed-up glass or stone. It can be blown or compressed into walls, and it has different R-values. It is also fire retardant and helps to protect buildings from destruction. This gives emergency services more time and allows them to reach the building and save lives.

Thermal conductivity is denoted as l displaystyle lambda , is not the same as thermal resistance. The latter is a measure of the rate at the which heat is transferred by physical movement. Thermal conductivity refers to a material’s ability to transmit energy via diffusion of free-moving electrons. It is for this reason that the conductivity in pure metals decreases when they are heated.

Plastics

Most plastics are very low in thermal conductivity, compared to metallic materials. In turn, they are excellent insulators. They also have a large specific heat capacity.

Plastics are poor heat conductors because they do not have electrons that can be used for conduction like metals. They can effectively resist heat transfer by creating an insulating air space.

Foam insulation products made of plastics such as expanded or extruded polystyrene (more commonly known as styrofoam) and silica aerogel are good examples. R-values for these types of foams can change over time, however, as some of the low-conductivity gas escapes and air replaces it - a process called thermal drift.

Metals

Like the bubbles found in Styrofoam, or the feathers of a snowsuit that obstructs convective flow, many insulating material trap air-filled pocket to obstruct pathways. This allows the materials to resist both convective and conductive heat flows. Bubble wraps and foams made with expanded or expended polystyrene as well silica-aerogel and natural fibers including cellulose, rock wool and slag are perfect for this. Fur and clothing are also good insulators.

The thermal conductivity (l) of a material can be defined as l=k0, where the characteristic constant k0 and l depend on temperature. The value l of a material is often used to determine its insulating capabilities. A low l is an indicator of a good insulator. However, a large l is associated with a poor insulator. This relationship is reflected through the R-values (or U-values) of building material.