The density of the foam is the measurement of the weight per unit volume. Expressed in kg/m³, density is the second important property of the foam and is a function of the chemicals used to produce the foam. The best foam is the foam to which no additives or fillers have been added to increase density. Flexible foams can be produced at any desired density. Net and gross densities are determined with laboratory samples. Gross density is determined by dividing the mass of the sample by its volume. Net density is determined by dividing the weight of ILD or CLD samples by the volume. While doing this process, there is a difference between net bottom density, net middle density, and net top density. The density at the bottom of the foam block is the highest compared to other regions. Density is measured and conditioned in accordance with TS 1975 standards. The density value is the key indicator of foam performance in terms of comfort, support, and durability. At the same time, it is the most important parameter affecting the foam price. Since high-density foam is produced using more material, its support for weight is higher. Load carrying capacity is higher. It should not be forgotten that foam hardness is independent of foam density. High-density foams can be produced very soft. Low-density ones can also be produced very hard. Density can be changed with the addition of cheap foam additives or fillers. Additives can be used to increase density, give a sense of comfort, or improve the sense of support, but they can negatively affect other foam properties such as tear resistance, air permeability, and durability.