Short definition of some words used to define  the physical characteristics of polyurethane foams.
The density is the volume weight of the foam, normally expressed in kilograms per cubic meter (kg./m3). The widest range of polyurethane foam goes from  18 to 50 kg/m3.
The density is not a measure of hardeness as for foams coming for latex.
The support is the measure of resistance to a load in expressed in Newton : 323 per square centimeter to a given percentage of compression of the foam. To obtain the value you must press the sample of foam with a 323 cm2 plate (the sample has to be bigger of the plate) up to the percentage prefixed from the thickness of the sample. You can read the necessary force for compression. Usually you are given 2 supporting rates corresponding to the compressions of the sample at 25% and at 65% of its original thickness. For example a value of 130 newton at 25% shows that you need to apply a force of 130 Newton to compress a sample of foam of 25% of its original thickness (that is bringing the thickness from 100 mm up to 75 mm). It follows that the higher is the vale and “harder” is the foam and vice versa.
Also the resistance to the compression is a measure of resistance to a load and it is generally espresse in Kilo pascal to a specific deflexed foam (usually 40% of its original thickness). The surface of the sample must be smaller that the pressing plate. The Higher is the value “harder” is the foam and vice versa.
The sample of the foam is put to repeated cycles of compression and decompression (dynamic stress). At the end of the cycle the support test is effected again that gives a lower value than the one obtained before the cycle. The difference from the original support and the one after the stress is expressed in percentage. The Lower is the value better is the foam.
The ultimate strength is the measure of the stress necessary to break the foam. The unit of measure is Pascal. The higher is the value more resistant is the foam. The test of the stretching it is realized together with the ultimate strength. The higher is the value the better is the foam.
The resistance to the rip is the measure of the required force to continue the rip in a foam with a preexisting cutting. It is expressed in Newton per meter (N/m). this propriety is important when the foam has to be applied to other supports (for example wood) by staples… The higher is the value the better is the foam.
The compression set is the measure for deforming the foam after a pressure for a certain period to a certain temperature. During the test the sample is compressed to a certain percentage of its original thickness. The loosing of the thickness is then expressed in percentage. The lower is the value the better is the foam.
The resilience is the measure of the elasticity of the foam. During this test a steel sphere is drop on the sample from a specific height. the height reached by the same after having rebounded on the foam is expressed in percentage. On very soft foams this test can give a lower value than the real one. The higher is the value the better is the foam.
These models can be reviewed with different density and viscosity polyurethane.

Memo Breeze

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