Thermal Load Stability
Oxidizing decay of organic components in thermal insulation boards increases with rising temperatures. Continuous thermal load is defined by the temperature at which the application of a particular grade can be technically and economically justified, so that the lifetime will extend to several years.

    Heat Coefficient
Marked with the symbol l this is one of the most important factors in thermal insulation boards - the spec sheet expresses it as W/mK. Low values in all grades make this insulation effective.

   Dimensional Stability at Continuous Thermal Load
Most insulation grades are made of an organic base. Compared to inorganic materials, these have the advantage of being much tougher and suited to withstand thermal stress without the tendency for cracking. On the other hand, in organic materials thermal stability decreases with time, which means although there is no sudden softening, disintegration or melting, their lifetime diminishes with rising temperatures. The dimensional stability under continuous thermal load is a very important criterion for thermal insulation or machine components. This is defined as the temperature at which the material does not shrink more than one percent after 5,000 hours of exposure.
An organic material rated at 450xF temperature stability at room temperature will only be dimensionally stable up to 390xF while under continuous thermal load. An inorganic material rated 156xF also will dimensionally stable up to 1,560xF.

  Compressive Strength at Maximum Operating Temperature
Compressive strength of materials is usually measured at room temperature, which is 20xC (68xF). It is generally known that this factor goes down with higher temperatures. In practice, compressive loads are usually much lower - a built-in safety factor.
The same organic material with a dimensional stability of 390xF will have a compressive strength of 300 N/mm² at room temperature, but only 100 N/mm² at 390xF.
The inorganic material of 1,560xF only has a compressive strength of 10N/mm² at room temperature, which remains the same under continuous thermal load.
Grade selection has to be based on specifications given for the equipment and production process - such as operating pressures and temperatures. Manufacturers of insulation furnish charts to aid with this selection.

   Moisture Absorption
Moisture absorption is a disadvantage in thermal insulation boards for two reasons. First of all, boards with high moisture content develop steam pressure at temperatures above 100xC (212xF), which may cause cracking, as often observed in boards with more than 10 percent moisture absorption. Secondly, the effectiveness of thermal insulation is significantly reduced, even though it is not noticeable while measuring the coefficient. A dry board, of course, has a more favorable coefficient than saturated material. If saturation occurs after every cooling cycle, additional heat is consumed during each heating cycle to evaporate the absorbed moisture.

   Tolerances
Fiber-reinforced synthetics cannot be compared with metallic materials as far as tolerances and dimensional stability are concerned. For economic reasons and considering that an insulation panel cannot possibly retain its absolute dimension once in operation, demands regarding tolerances should be reasonable. It should be mentioned that thermal insulation panels are rarely ever used at room temperature. Change of dimension does not occur through thermal expansion, but through permanent changes such as drying, post-curing processes, long-term oxidative decay, etc. Nevertheless, most panel grades can be supplied with a parallelism of q0.05 mm = 1/500 inch.

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