Definition of Foam
Meaning of the Term as it Pertains to Mattresses
What is Foam?
A material made from latex or polyurethane, foam features thousands of tiny pockets of air. The air-pocket design, known as a cellular structure, gives foam a spongy, cushion-like quality. During production, manufacturers can adjust foam density to be as pillowy or as solid as desired, which makes the material ideal for use in bedding. Mattresses commonly use soft foam for top comfort layers and dense foam for solid core support systems. Mattresses may feature foam elements or be entirely made of foam.
An entirely foam mattress uses visco-elastic foam, which we know as memory foam. The highly engineered foam compresses slowly when initial pressure is applied and forms to the shape of the body resting on it. In addition to responding to pressure, memory foam reacts to heat by drawing excess warmth away from the body.
Foam can have open-cell or closed-cell composition. Closed-cell foams have closed cell structures, meaning that air is sealed in the individual air pockets. Open-cell foam has tiny "holes" in the cell walls, which allows air to pass through the material. Most foam mattresses use open-cell foam because of its breathability, which keeps the sleep surface cool and inhibits the growth of mold and mildew.
A term that describes when foam losses its ability to support a certain load capacity. Foam typically experiences fatigue after prolonged use or if excessive weight is applied to the mattress. If top comfort layers begin to fatigue, overall comfort may diminish, resulting in less satisfying rest. If foam support experiences fatigue, a mattress will sag or bow out, which causes unhealthy back support.
Foam fatigue is relatively uncommon with mattresses. If foam fatigue does occur, it typically affects comfort layers that have worn out after years of extended use. Memory foam is considerably sturdy, and there are few reports of foam fatigue with the mattress type. Most memory foam mattresses have warranties that protect against mattress fatigue and other malfunctions. Warranties often last from 10 to 25 years. Memory foam mattresses that experience foam fatigue will most likely be cheap, low-quality products that, in all probability, do not have warranties.
How solid or compacted foam is. Calculated by dividing the weight of a piece of foam by the multiplication of its length, width, and height. Density can be expressed by pounds per cubic foot (lbs./ft^3) or simply by weight (lbs.), with pcf assumed. A higher foam density means a mattress uses more foam material and can support a greater amount of weight before experiencing fatigue. Foam density should not be confused with firmness. High-density foam can have a soft comfort level, and vice versa. Density also effects foam durability, with higher densities lasting longer.
Foam density falls in three categories: low-density, medium-density, and high-density. About 2.5 - 3 lbs., low-density foam is typically the cheapest foam density because it requires the least amount of material to produce. Reasonably priced medium-density foam weighs about 4 lbs. per cubic foot and can resist enough pressure to hold just about anyone. Top-of-the-line high-density foam has 5 lbs. density and above. Medium- and high-density foams tend to last longer and provide greater support than low-density foam.
Also see discoloration. Foam discoloration describes when foam materials exhibit unattractive yellow tints. Technically known as phenolic yellowing, foam discoloration occurs gradually over time when foam is exposed to light. The phenomenon occurs when anti-oxidants used in manufacturing foam oxidize. Exposure to sunlight accelerates discoloration, but any light source will cause foam to change color over time. Though unappealing visually, discoloration does not affect the performance or longevity of a mattress. A discolored mattress may provide quality sleep decades after discoloring.
Keeping mattresses covered with linens will prevent discoloration. As mentioned, light causes discoloration, so limiting the amount of time a mattress is hit by light will preserve it from discoloration. This precaution will only affect the aesthetic of the mattress and will not prolong its life.