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Thermal conductivity depends on the material and for fluids, its temperature and pressure. For comparison purposes, conductivity under standard conditions (20 °C at 1 atm) is commonly used. For some materials, thermal conductivity may also depend upon the direction of heat transfer.
This is a list of insulation materials used around the world.. Typical R-values are given for various materials and structures as approximations based on the average of available figures and are sorted by lowest value.
In heat transfer, the thermal conductivity of a substance, k, is an intensive property that indicates its ability to conduct heat. For most materials, the amount of heat conducted varies (usually non-linearly) with temperature.
Thermal insulators are materials that inhibit the migration of heat. For electrical insulators, materials that inhibit the migration of electric current, ...
Some insulator manufacturers stopped making glass insulators in the late 1960s, switching to ceramic materials. Some electric utilities use polymer composite materials for some types of insulators. These are typically composed of a central rod made of fibre reinforced plastic and an outer weathershed made of silicone rubber or ethylene ...
Bulk insulators block conductive heat transfer and convective flow either into or out of a building. Air is a very poor conductor of heat and therefore makes a good insulator. Insulation to resist conductive heat transfer uses air spaces between fibers, inside foam or plastic bubbles and in building cavities like the attic.
The R-value test measures heat transfer through the material, not to or from its surface. There is no standard test designed to measure the reflection of radiated heat energy alone. Radiated heat is a significant means of heat transfer; the sun's heat arrives by radiating through space and not by conduction or convection.
An example of this scenario is a building on a cold winter day; the solid material in this case is the building wall, separating the cold outdoor environment from the warm indoor environment. According to the second law of thermodynamics, heat will flow from the hot environment to the cold one as the temperature difference is equalized by ...