Thermal conductivity of building materials: what does the indicator mean + table of values

Alexey Dedyulin
Checked by a specialist: Alexey Dedyulin
Author: Victor Kitaev
Last update: May 2019

The construction business involves the use of any suitable materials. The main criteria are safety for life and health, thermal conductivity, reliability. The following are price, aesthetics, versatility, etc.

Consider one of the most important characteristics of building materials - the coefficient of thermal conductivity, since it is precisely on this property that, for example, depends on the level of comfort in the house.

What is KTP building material?

Theoretically, and practically the same, with building materials, as a rule, two surfaces are created - external and internal. From the point of view of physics, a warm region always tends to a cold region.

In relation to building material, heat will tend from one surface (warmer) to another surface (less warm). Here, in fact, the ability of a material with respect to such a transition is called the thermal conductivity coefficient or, in the abbreviation, KTP.

What is the thermal conductivity coefficient?
Scheme explaining the effect of thermal conductivity: 1 - thermal energy; 2 - thermal conductivity coefficient; 3 - temperature of the first surface; 4 - temperature of the second surface; 5 - thickness of building material

The characteristic of a transformer substation is usually based on tests, when an experimental specimen of 100x100 cm is taken and the thermal effect is applied to it, taking into account a temperature difference of two surfaces of 1 degree. The exposure time is 1 hour.

Accordingly, thermal conductivity is measured in watts per meter per degree (W / m ° C). The coefficient is indicated by the Greek symbol λ.

By default, the thermal conductivity of various materials for construction with a value of less than 0.175 W / m ° C, equates these materials to the category of insulating materials.

Modern production has mastered the technology of manufacturing building materials, the level of KTP which is less than 0.05 W / m ° C.Thanks to such products, it is possible to achieve a pronounced economic effect in terms of energy resources consumption.

Influence of factors on the level of thermal conductivity

Each individual building material has a specific structure and has a kind of physical condition.

The basis of this are:

  • dimension of crystals of the structure;
  • phase state of the substance;
  • degree of crystallization;
  • anisotropy of the thermal conductivity of crystals;
  • volume of porosity and structure;
  • heat flow direction.

All these are factors of influence. The chemical composition and impurities also have a certain effect on the level of KTP. The amount of impurities, as practice has shown, has a particularly expressive effect on the level of thermal conductivity of crystalline components.

Insulating building material
Insulating building materials - a class of products for construction, created taking into account the properties of KTP, close to optimal properties. However, achieving perfect thermal conductivity while maintaining other qualities is extremely difficult

In turn, the KTP is influenced by the operating conditions of the building material - temperature, pressure, humidity, etc.

Building materials with minimal KTP

According to studies, the minimum value of thermal conductivity (about 0.023 W / m ° C) has dry air.

From the point of view of the use of dry air in the structure of a building material, a design is needed where dry air resides inside numerous enclosed spaces of small volume. Structurally, such a configuration is represented in the image of numerous pores within the structure.

Hence the logical conclusion: building materials, the internal structure of which is a porous formation, must have a low level of KTP.

Moreover, depending on the maximum permissible porosity of the material, the value of thermal conductivity approaches the value of the thermal transfer coefficient of dry air.

Porous structure of building material
The creation of a building material with minimal thermal conductivity is facilitated by the porous structure. The more pores of different volumes are contained in the structure of the material, the better KTP is acceptable to obtain

In modern production, several technologies are used to obtain the porosity of the building material.

In particular, the following technologies are used:

  • foaming;
  • gas formation;
  • water supply;
  • swelling;
  • introduction of additives;
  • create fiber frames.

It should be noted: the coefficient of thermal conductivity is directly related to such properties as density, heat capacity, thermal conductivity.

The value of thermal conductivity can be calculated by the formula:

λ = Q / S * (T1-T2) * t,


  • Q - The amount of heat;
  • S - material thickness;
  • T1, T2 - temperature on both sides of the material;
  • t - time.

The average density and thermal conductivity are inversely proportional to the porosity. Therefore, based on the density of the structure of the building material, the dependence of thermal conductivity on it can be calculated as follows:

λ = 1.16 √ 0.0196 + 0.22d2 – 0,16,

Where: d Is the density value. This is the formula of V.P. Nekrasov, demonstrating the influence of the density of a particular material on the value of its KTP.

The effect of moisture on the thermal conductivity of building materials

Again, judging by examples of the use of building materials in practice, the negative effect of moisture on the construction materials of the building materials is revealed. It is noticed - the more moisture the building material is subjected to, the higher the value of the KTP becomes.

Wet building material
In various ways, they seek to protect the material used in construction from moisture. This measure is justified, given the increase in the coefficient for wet building material

Justifying such a moment is not difficult. The effect of moisture on the structure of the building material is accompanied by humidification of the air in the pores and partial replacement of the air.

Given that the parameter of the thermal conductivity coefficient for water is 0.58 W / m ° C, a significant increase in the thermal conductivity of the material becomes clear.

It should also be noted a more negative effect, when water entering the porous structure is additionally frozen - it turns into ice.

Accordingly, it is easy to calculate an even greater increase in thermal conductivity, taking into account the parameters of the KTP of ice, equal to the value of 2.3 W / m ° C. An increase of about four times to the thermal conductivity of water.

Winter building
One of the reasons for the abandonment of winter construction in favor of construction in the summer should be considered precisely the factor of the possible freezing of certain types of building materials and, as a result, increased thermal conductivity

From this, the construction requirements regarding the protection of insulating building materials from moisture penetration become apparent. After all, the level of thermal conductivity increases in direct proportion to quantitative humidity.

No less significant is another point - the opposite, when the structure of the building material is subjected to significant heating. Excessively high temperature also provokes an increase in thermal conductivity.

This happens due to an increase in the kinematic energy of the molecules that make up the structural basis of the building material.

True, there is a class of materials, the structure of which, on the contrary, acquires the best properties of thermal conductivity in the regime of strong heating. One such material is metal.

Metal heating and thermal conductivity
If, under strong heating, most of the widespread building materials change the thermal conductivity upward, strong heating of the metal leads to the opposite effect - the metal thermal transfer coefficient decreases

Coefficient determination methods

Different methods are used in this direction, but in fact all measurement technologies are combined by two groups of methods:

  1. Stationary measurement mode.
  2. Non-stationary measurement mode.

The stationary technique implies working with parameters that are unchanged over time or vary insignificantly. This technology, judging by practical applications, allows counting on more accurate results of KTP.

The actions aimed at measuring thermal conductivity, the stationary method can be carried out in a wide temperature range - 20 - 700 ° C. But at the same time, stationary technology is considered time-consuming and complex technique, requiring a large amount of time for execution.

Thermal conductivity meter
An example of an apparatus designed to perform measurements of the thermal conductivity coefficient. This is one of the modern digital designs that provides fast and accurate results.

Another measurement technology is non-stationary, it seems more simplified, requiring 10 to 30 minutes to complete the work. However, in this case, the temperature range is significantly limited. Nevertheless, the technique has found wide application in the manufacturing sector.

Table of thermal conductivity of building materials

It makes no sense to measure many existing and widely used building materials.

All these products, as a rule, have been tested repeatedly, on the basis of which a table of thermal conductivity of building materials has been compiled, which includes almost all the materials necessary for the construction site.

One of the options for such a table is presented below, where KTP is the thermal conductivity coefficient:

Material (building material)Density, m3KTP dry, W / mºC% humid_1% humid_2KTP at damp_1, W / m ºCKTP at damp_2, W / m ºC
Roofing bitumen14000,27000,270,27
Roofing bitumen10000,17000,170,17
Roofing slate18000,35230,470,52
Roofing slate16000,23230,350,41
Roofing bitumen12000,22000,220,22
Asbestos cement sheet18000,35230,470,52
Asbestos cement sheet16000,23230,350,41
Asphalt concrete21001,05001,051,05
Building Roofing6000,17000,170,17
Concrete (on a gravel pad)16000,46460,460,55
Concrete (on a slag cushion)18000,46460,560,67
Concrete (on gravel)24001,51231,741,86
Concrete (on a sand cushion)10000,289130,350,41
Concrete (porous structure)10000,2910150,410,47
Concrete (solid structure)25001,89231,922,04
Pumice concrete16000,52460,620,68
Construction bitumen14000,27000,270,27
Construction bitumen12000,22000,220,22
Lightweight mineral wool500,048250,0520,06
Mineral wool heavy1250,056250,0640,07
Mineral wool750,052250,060,064
Vermiculite leaf2000,065130,080,095
Vermiculite leaf1500,060130,0740,098
Gas-foam-ash concrete8000,1715220,350,41
Gas-foam-ash concrete10000,2315220,440,50
Gas-foam-ash concrete12000,2915220,520,58
Gas foam concrete (foam silicate)3000,088120,110,13
Gas foam concrete (foam silicate)4000,118120,140,15
Gas foam concrete (foam silicate)6000,148120,220,26
Gas foam concrete (foam silicate)8000,2110150,330,37
Gas foam concrete (foam silicate)10000,2910150,410,47
Gypsum slab12000,35460,410,46
Expanded clay gravel6002,14230,210,23
Expanded clay gravel8000,18230,210,23
Granite (basalt)28003,49003,493,49
Expanded clay gravel4000,12230,130,14
Expanded clay gravel3000,108230,120,13
Expanded clay gravel2000,099230,110,12
Shungizite gravel8000,16240,200,23
Shungizite gravel6000,13240,160,20
Shungizite gravel4000,11240,130,14
Wood pine transverse fiber5000,0915200,140,18
Glued plywood6000,1210130,150,18
Pine tree along the fibers5000,1815200,290,35
Oak Tree Across the Fibers7000,2310150,180,23
Duralumin Metal260022100221221
Reinforced concrete25001,69231,922,04
Tuff concrete16000,527100,70,81
Mortar with sand17000,52240,700,87
Sand for construction work16000,035120,470,58
Tuff concrete18000,647100,870,99
Facing cardboard10000,185100,210,23
Laminated board6500,136120,150,18
Foam rubber60-950,0345150,040,054
Expanded clay14000,475100,560,65
Expanded clay16000,585100,670,78
Expanded clay18000,865100,800,92
Brick (hollow)14000,41120,520,58
Brick (ceramic)16000,47120,580,64
Tow construction1500,057120,060,07
Brick (silicate)15000,64240,70,81
Brick (solid)18000,88120,70,81
Brick (slag)17000,521,530,640,76
Brick (clay)16000,47240,580,7
Brick (trepelny)12000,35240,470,52
Metal copper850040700407407
Dry plaster (sheet)10500,15460,340,36
Mineral wool slabs3500,091250,090,11
Mineral wool slabs3000,070250,0870,09
Mineral wool slabs2000,070250,0760,08
Mineral wool slabs1000,056250,060,07
PVC linoleum18000,38000,380,38
Foam concrete10000,298120,380,43
Foam concrete8000,218120,330,37
Foam concrete6000,148120,220,26
Foam concrete4000,116120,140,15
Foam concrete on limestone10000,3112180,480,55
Foam concrete on cement12000,3715220,600,66
Expanded polystyrene (PSB-S25)15 – 250,029 – 0,0332100,035 – 0,0520,040 – 0,059
Expanded polystyrene (PSB-S35)25 – 350,036 – 0,0412200,0340,039
Polyurethane foam sheet800,041250,050,05
Polyurethane foam panel600,035250,410,41
Lightweight foam glass2000,07120,080,09
Weighted foam glass4000,11120,120,14
Pearlitic cement slab2000,041230,0520,06
Ash Gravel Concrete14000,47580,520,58
Plate of fiberboard (chipboard)2000,0610120,070,08
Plate of fiberboard (chipboard)4000,0810120,110,13
Plate of fiberboard (chipboard)6000,1110120,130,16
Plate of fiberboard (chipboard)8000,1310120,190,23
Plate of fiberboard (chipboard)10000,1510120,230,29
Portland cement polystyrene concrete6000,14480,170,20
Vermiculite concrete8000,218130,230,26
Vermiculite concrete6000,148130,160,17
Vermiculite concrete4000,098130,110,13
Vermiculite concrete3000,088130,090,11
Fiberboard plate8000,1610150,240,30
Metal steel785058005858
Glass wool500,048250,0520,06
Fiberboard plate6000,1210150,180,23
Fiberboard plate4000,0810150,130,16
Fiberboard plate3000,0710150,090,14
Glued plywood6000,1210130,150,18
Reed plate3000,0710150,090,14
Cement-sand mortar18000,58240,760,93
Metal cast iron720050005050
Cement-slag mortar14000,41240,520,64
Complex sand solution17000,52240,700,87
Dry plaster8000,15460,190,21
Reed plate2000,0610150,070,09
Cement plaster10500,15460,340,36
Peat plate3000,06415200,070,08
Peat plate2000,05215200,060,064

We also recommend reading our other articles, where we talk about how to choose the right insulation:

  1. Insulation for the attic roof.
  2. Materials for warming the house from the inside.
  3. Insulation for the ceiling.
  4. Materials for external thermal insulation.
  5. Insulation for the floor in a wooden house.

Conclusions and useful video on the topic

The video is thematically directed, which explains in sufficient detail what KTP is and “what it is eaten with”. After reviewing the material presented in the video, there are high chances to become a professional builder.

The obvious point is that a potential builder needs to know about thermal conductivity and its dependence on various factors. This knowledge will help to build not just high quality, but with a high degree of reliability and durability of the object. Using the coefficient in essence is a real saving of money, for example, in paying for the same utility services.

If you have questions or have valuable information on the topic of the article, please leave your comments in the box below.

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Visitors Comments
  1. Phill

    Wow, what an old-slate, it turns out, reliable in this regard. I already thought cardboard removes more heat. Still, there is nothing better than concrete, as for me. Maximum heat and comfort, do not care about humidity and other negative factors. And if concrete + slate, then in general fire 🙂 just torment it, you’re tormented by it, now they make it so dull in quality ..

  2. Sergei

    Our roof is covered with slate. In summer, it is never hot at home. It looks unpretentious, but better than metal or roofing iron. But we did not do it because of the numbers. In construction, you need to use a proven methodology and be able to choose the best in the markets with a small budget. Well, and evaluate the operating conditions of housing.Sochi residents do not need to build houses ready for forty degree frosts. It will be in vain wasted funds.