Enumerating the parameters of heaters, the thermal conductivity of the material is always put in the first place. It depends on how much air is contained in this substance. After all, it is the air environment that serves as an excellent natural heat insulator. Note that the ability to conduct heat decreases with increasing rarefaction of the medium. So it is best to keep the heat layer from the vacuum. The work of thermoses is based on this principle. But during construction it is problematic to create a vacuum, therefore they are limited to ordinary air. For example, the low thermal conductivity of expanded polystyrene, especially extruded, is due to the fact that there is more than enough of this air in it.

Thermal conductivity of extruded polystyrene foam

What affects the ability of expanded polystyrene to conduct heat

In order to clearly understand what thermal conductivity is, we take a piece of material of a meter thickness and an area of ​​one square meter. Moreover, we heat one side of it, and leave the other cold. The difference in these temperatures should be ten times. By measuring the amount of heat, which in one second goes to the cold side, we obtain the coefficient of thermal conductivity.

Why is polystyrene foam capable of retaining both heat and cold well? It turns out that the whole thing is in its structure. Structurally, this material consists of many sealed multifaceted cells having a size of 2 to 8 millimeters. Inside, they have air - it is 98 percent and serves as an excellent heat insulator. Polystyrene accounts for 2% of the volume. And by weight polystyrene is 100%, because air, relatively speaking, has no mass.

It should be noted that the thermal conductivity of the extruded polystyrene foam remains unchanged over time. This compares this material favorably with other foams whose cells are filled not with air but with another gas. After all, this gas has the ability to gradually evaporate, and the air remains inside the sealed polystyrene foam cells.

When buying foam, we usually ask the seller what the density of this material is. After all, we are used to the fact that density and the ability to conduct heat are inextricably linked with each other. There are even tables of this dependence, with which you can choose the appropriate brand of insulation.

Density of expanded polystyrene kg / m3Thermal Conductivity W / MKV
10 0,044
15 0,038
20 0,035
25 0,034
30 0,033
35 0,032

However, at present, they have come up with an improved insulation, in which graphite additives are introduced. Thanks to them, the coefficient of thermal conductivity of expanded polystyrene of various densities remains unchanged. Its value is from 0.03 to 0.033 watts per meter per Kelvin. So now, acquiring a modern advanced EPSP, there is no need to check its density.

Marking of expanded polystyrene whose thermal conductivity is independent of density:

Styrofoam brandThermal Conductivity W / MKV
EPS 50 0.031 - 0.032
EPS 70 0.033 - 0.032
EPS 80 0.031
EPS 100 0.030 - 0.033
EPS 120 0.031
EPS 150 0.030 - 0.031
EPS 200 0.031

Expanded polystyrene and other heaters: comparison

Let us compare the thermal conductivity of mineral wool and polystyrene foam. For the latter, this indicator is less and ranges from 0.028 to 0.034 watts per meter per Kelvin. The thermal insulation properties of EPSS without graphite additives decrease with increasing density. For example, extruded polystyrene foam, whose thermal conductivity is 0.03 watts per meter per Kelvin, has a density of 45 kilograms per cubic meter.

Comparing these indicators for a variety of heaters, we can conclude in favor of EPS. A two-centimeter layer of this material holds heat in the same way as mineral wool with a layer of 3.8 centimeters, ordinary polystyrene with a layer of 3 centimeters, a wooden board 20 cm thick. Brick but it’s necessary to lay out a wall 37 centimeters thick, and foam concrete - 27 centimeters.Impressive, isn't it?


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