The density of a material is an important consideration when using foot orthotics as materials of different densities will have different biomechanical affects. A lower density material will be used more for cushioning and shock absorption whereas a higher density material will be used more for deflection and support.
Density is a measure of the mass per unit of volume of a material; that is, how much mass there is in a particular space. The International System of Units (SI) unit of density is the kilogram per cubic meter (kg/m3). The unit of gram per cubic centimetre (g/cm3) is also often used (one g/cm3 is equal to 1000 kg/m3). Pounds per cubic foot (lbs/ft3) is still sometimes used in the USA.
The formula is ρ = m/V, where ρ (rho) is the density, m is the mass, and V is the volume.
For example, the EVA foams that are often used in foot orthotic manufacture are available in a wide range of different densities. A higher density EVA may be 350 to 400kg/m3 and a lower density one may be 35kg/m3. The medical grade Poron is available two densities: 240 and 320 kg/m3 (15 and 20 lb/in3).
Polypropylene has a density of about 1175 kg/m3. Air has a density of 1.2 kg/m3 at sea level. Gold is 19 320 kg/m3.
ISO standard 12154:2014 or ASTM standard D3574 are used as the standards for the testing and measurement of material density .
Related Topics:
Material hardness | Shore durometer | Compression set | Material stiffness | Material properties | Foot orthotic materials | Durability
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