Research into foam durability by measuring flex fatigue, or the loss of foam firmness after flexing the foam a predetermined number of cycles, shows that as polymer density increases, firmness loss is lessened. Less firmness lose means that, for example, seat cushions still feel "new" and that mattresses retain their original "feel." Higher density foams also better retain their ability to provide support. Other factors used to gauge foam durability also improve as density increases. One of these is compression set, or the tendency of foam to lose height as it is used. As density increases, height loss decreases dramatically, which means that the fabric on furniture cushions stays taut and that mattresses don't get body impressions. In fact, may mattress manufactures have increased the densities of their quilting foam during the past few years to reduce instances of body impressions in innerspring as well as foam mattresses.

 

The Role of Foam Additives and Fillers

As noted before, overall foam density can be affected by additives and filling materials used to manufacture different foams. In some cases, additives are used to improve the combustion performance of foams. The most common occurrence of this is when additives are used to allow conventional polyurethane foams to meet the combustibility requirements of California Technical Bulletin 117 for residential furniture. Additive requirements to meet this regulation are relatively minor, but they can affect overall foam density. To meet stringent combustibility requirements, greater amounts of additives or filling materials are needed. For example, foams that meet California Technical Bulletin 133, the Boston Fire Code, or similar stringent requirements have large amounts of additives that can increase the foam's density by over a pound per cubic foot. Additives are used to increase foam density for other reasons. Additives may be used to increase the overall weight of the cushion, which gives the cushion a heavier, more luxurious feel, or additives and fillers can be used to simply increase the ability of the foam to provide support. Various materials are used as additives to increase density. However, it is important to note that while additives may increase density, and in some cases improve support, they may not improve other properties of the foam. Additives can make foams more likely to tear, and can reduce foam durability. This is because additives, since they are not part of the actual foam cellular structure, can act as abrasives that break down foam cell walls, making foam lose more of its original properties through use. Therefore it is important that when you select foams for different applications, you look at the polymer, or unfilled, density of the foam being used.

 

Summary

1. Density, measured in pounds per cubic foot, is a key property for determining flexible polyurethane foam performance. 2. Foam density is independent of foam firmness. 

3. Density relates to the comfort, support and durability properties of the foam.

4. Density can be affected by foam additives or fillers. To truly gauge foam performance, the unfilled, or polymer density of the foam must be evaluated. Polymer density takes only the weight of the basic foam materials into account.

5. Foam fillers and additives are used to improver the combustion performance of the foam, to make the cushion feel heavier and more luxurious, or to improve support, but may have a negative effect on other foam properties.