Why there? Today I talked to you about thermo-conactivity and thermal resistance. Every material just has a specific color and a specific weight, has a specific thermal conductivity. Okay, what exactly is thermal conductivity? Let's have a look at heat transfer. Conduction is one fraction of heat transfer. A good example for conduction is a hot kettle. Out. Convection is another fraction of heat transfer and that is heat moving with air. A good example for this is a hair dryer. Radiation, the last fraction is heat transferred by electromagnetic waves. And it's me two weeks from now. Thermo-conactivity can be measured with an apparatus like this where a specimen is put between plates of a different temperature. It's simplified terms, the heat as it is traveling through the specimen is recorded and if the distance and the temperature differential are known, it is possible to calculate the thermal conductivity from this, which is given in what per meter Kelvin. To give you an idea of magnitude vacuum insulation panel, it starts at about 0.004, what per meter Kelvin? Typical insulation is about 10 times of that 0.04 and software Timmer is three times that again, so 30 times that of vacuum insulation panels. The value for reinforced concrete is about 18 times higher than software and the value for aluminum about 1800 times. Thermo-conactivity is the property of a material and the symbols used are either lower case lambda or lower case k, but the unit is always what per meter Kelvin and the brackets are essential. Thermo-resistance in contrast is the property of a layer and the symbol used is upcase r and the unit is square meter times Kelvin or what? r is calculated by putting the layer thickness over the thermo-conactivity of the material. Let's do an example. Supposedly we have a 40 centimeter thick support Timmer slab, so the 40 centimeters is the distance that goes on top of the bar and then the thermo-conactivity of 0.1 to what per meter k below and as we are dividing the meter k go on top of the bar again that gives us a resistance of 3.333 square meter times Kelvin over what? The same layer and aluminum has still the same thickness but the thermo-conactivity is markedly different and so as a result only 0.002 square meter times Kelvin over what? And these are our values which stands for thermo-resistance and that's all you need to know about thermo-conactivity and thermo-resistance. In another video I talk about surface resistance and u-value calculation. Thanks for watching!