Thermal Conductivity - Air Cavities

The Aeroblock design takes advantage of large voids to create a greater thermal barrier.

There is a typical misconception that air is not a good insulator. The fact is that air is a poor conductor of energy and has one of the lowest K values for ordinary substances. A void in a material WILL NOT TRANSMIT HEAT as much as the material surrounding it.

Since air is not structural it cannot be used by and in itself. The fact is that expanded polystyrene gets it low K value from the trapped air and not the plastic itself.

The design of a good block will try to create thermal bridges that offer the maximum resistance.

Thermal bridge

Thermal bridges are points in the building envelope that allow heat conduction to occur. Since heat flows through the path of least resistance, thermal bridges can contribute to poor energy performance. . A thermal bridge is created when materials that are poor insulators come in contact.

In physics, thermal conductivity, k, is the intensive property of a material that indicates its ability to conduct heat. It is used primarily in Fourier's Law for heat conduction.

It is defined as the quantity of heat, Q, transmitted during time t through a thickness L, in a direction normal to a surface of area A, due to a temperature difference ΔT, under steady state conditions and when the heat transfer is dependent only on the temperature gradient.

thermal conductivity = heat flow rate × distance / (area × temperature difference)

Alternately, it can be thought of as a flux of heat (energy per unit area per unit time) divided by a temperature gradient (temperature difference per unit length)

Typical units are SI: W/(m*K) and Imperial units: (btu*ft)/(hr*(ft^2)*F). To convert between the two, use the relation 1 (btu*ft)/(hr*(ft^2)*F) = 1.730735 W/(m*K).

This is a list of approximate values of thermal conductivity, k, for some common materials. Please consult the list of thermal conductivities for more accurate values, references and detailed information.

Material	k, [k] = W/(m*K)
Air	0.025
Alcohol or oil	0.15
Aluminium	237
Copper	401
Epoxy (unfilled)	0.19
Epoxy (silica-filled)	0.30
Gold	318
Lead	35.3
Silver	429
Cork	0.05
Diamond	900 – 2320
Glass	1.1
Rubber	0.16
Sandstone	2.4
Soil	0.15
Stainless steel	15
Thermal grease	0.7 – 3
Wood	0.04 – 0.4

Polystyrene
Density	1050 kg/m³
Specific Gravity	1.05
Electrical conductivity (s)	10-16 S/m
Thermal conductivity (k)	0.08 W/(m·K)
Young's modulus (E)	3000-3600 MPa
Tensile strength (st)	46–60 MPa
Elongation at break	3–4%
Notch test	2–5 kJ/m²
Glass temperature	95 °C
Melting point[1]	240 °C
Vicat B	90 °C[2]
Heat transfer coefficient (Q)	0.17 W/(m2K)
Linear expansion coefficient (a)	8 10-5 /K
Specific heat (c)	1.3 kJ/(kg·K)
Water absorption (ASTM)	0.03–0.1
Decomposition	± 2000 years[