The density is determined on all firefighting foam samples that are tested at Dyne. The density on a Dyne report is the amount of mass per given volume (g/mL). It is an important physical property that can quickly help identify any potential problems that might be occurring with the foam.

What is Density?
Density is defined as a quantity per given space, in other words, how much material is in a defined spaced. Most commonly, the density is reported as a mass per given volume as the quantity and space, respectively. To determine this density, you can measure the mass of a specific volume or vice versa (measure the volume of a specific mass). The calculated density would simply be the mass divided by the volume. At Dyne, we report the density with the units of g/mL which comes from this division – the amount of mass (g) per volume (mL). For example, the density of water at room temperature is about 0.998 g/mL. That means that if we poured out 1 mL of water, the mass of that water would be 0.998 g.

Notice that the temperature is noted when discussing density as the temperature does affect the volume in this calculation. While there are some exceptions, typically the higher the temperature the lower the density. The densities measured at Dyne and throughout the foam industry are measured in a precise temperature range to create consistency when comparing results. Keep this in mind when measuring densities in the field. While the differences may only be minor, measuring a density in the field at a different temperature than the literature may result in an incorrect comparison.

What does an “Out of Spec” Density mean on a Dyne Test Report?

Newly manufactured foam arrives on site with a specific density range, which can usually be viewed on the product’s data sheet. In an ideal situation, the density would never change from its original value since the foam manufacturer would want the same chemical makeup inside as when it left their manufacturing floor – this ensures the performance they intended. However, an “Out of Spec” density on a Dyne Test Report may indicate a change in the chemical makeup of the foam due to storage conditions, contamination, and aging. This change in physical property may lower the performance of the foam.

The changing of the chemical composition of that foam, for example, can affect performance which can be monitored using the density. For instance, if water gets into a foam concentrate storage container that had a density of 1.030 g/mL when purchased, the resulting density would now be lower since the water density is lower (0.998 g/mL). How low the result depends on the amount of water contamination. If the resulting pail was now 99+% water, you can imagine that the resulting density would also be 0.998 g/mL. The more water you add, the closer and closer the result gets 0.998 g/mL since the container gets closer and closer to just being entirely water.

This scenario can also be played out with other contamination, like sea water or mineral oil for instance. If the contaminate density is higher than that of the foam, you can expect the density of your foam to rise. Things can get complicated when multiple contaminations occur or the density of a contaminate is so close to the foam’s density that the impact is masked. Chemical reactions that may occur in the foam due to contamination, mixing of incompatible foam, or excessive heat for example, can also impact the density as these chemical reactions can create compounds with different densities than the original ingredient or even cause some ingredients to fall out of solution. Even solvent evaporation can change the density of the foam as the evaporated solvent’s mass is now lost from that volume.

For all of these reasons which can affect the performance of the foam and be seen in the density, manufacturers typically report a density range their foam should maintain on their product’s datasheet – any deviation from this range will result in an “Out of Spec” designation on a Dyne report. Keep in mind that while a density may be “Out of Spec” with this range, the ultimate pass/fail criteria is the foam’s performance. While you may see a density that is just slightly lower than the manufacturer’s range, the performance could still be enough to pass the performance requirements and the foam will receive a passing overall grade. Also keep in mind that “Out of Spec” designations might result from incorrect product information or mixing of two different foam products in the same tank, as each product may have a slightly different range depending on the ingredients the manufacturer used.

For an explanation on all physical properties and performance properties tested on firefighting foam samples, refer to Foam Testing Explanation LBTR-4054. If you have any questions, our chemists are always available to answer them. Call Dyne at (800) 632-2304 or email,, for assistance with understanding your test results.