Support is a key function of flexible polyurethane foam. In many ways, it is the most important function foam can provide.
The dictionary definition of support is to "carry weight of, hold up, keep from falling or sinking." In upholstery, good support from foam means that cushions don't "bottom out," "feel through" or compress to the point where they no longer hold up the weight of a person. It also means that the cushion is capable of distributing the weight of the person for maximum comfort.
The most common foam specifications are density and 25% IFD (firmness). However, it's also possible to choose the deep down support of the foam. This is done by specifying foam having compression modulus or support factor within available ranges as shown on the accompanying chart. In some ways, the compression modulus measurement may be a more valid measurement of foam's cushioning ability than other specifications because one sits deeper than 25% into a seat cushion.
Higher foam densities can provide increased support. Support capability often varies within ranges with different densities, types and grades of foam.
Some foam grades are formulated to have specific ranges of support.
A Definition of Compression Modulus (Support Factor)
Compression modulus is not a measurement unique to foam. It can be determined for other components, such as springs or webbing.
An explanation of how compression modulus is determined helps illustrate this. Compression modulus is the ratio of a foam's ability to support force at different indentation (or compression) levels. It is determined by taking the ratio of the foam's IFD at 25 percent indentation and 65 percent indentation (65%IFD:25% IFD).
The ratio of a foam that has a 25 percent IFD of 30 pounds and a 65 percent IFD of 60 pounds is 2.0. This is considered a typical level of support for most conventional polyurethane foams. The 65 percent IFD measurement, although rarely specified by foam purchasers, if key to evaluating support, because it can vary significantly from one type of foam to another. Compression modulus measurements for foam range from about 1.8 to 3.0.
In foam, two things effect support factor:
1. Foam density. Usually, the higher the density of the foam, the better its support.
2. Foam chemical formulations and the manufacturing process. Foam cell structure can effect support. Finehope can alter support by changing foam chemistry slightly, by utilizing specialty chemicals or by adjusting the manufacturing process. Fillers may be added during the formulation to increase support properties.
In recent years, a number of "high performance" foams have been developed by Finehope, apply on Anti fatigue mat field.