Foam is one of the most important elements of an upholstery project, but most people lack the vocabulary — or rather, the correct understanding of the vocabulary — to properly describe the kind of foam they want. Even designers and architects may know that they need to consider the foam’s density, but have no idea how it relates to other characteristics, such as firmness and cell structure.
To help you choose the right kind of foam for your business’s or client’s next project, we’ve explained the different qualities of foam and the importance of each.
Just like with other applications, foam density measures the mass or quantity of the material per a measurable volume or size.
However, density is measured differently depending on the material. For foam, the standard is to weigh a block measuring one foot on each side. A block that weighs 5 pounds would have a 5-pound density.
Foam’s density isn’t related to its firmness, but it is related to its durability and quality because more material is being compressed into a certain volume. This also means that denser materials will weigh more.
A density of 1 to 3 pounds is typical for most conventional foams, with lower-density foam being used for crafts, shipping foam, guest room mattress toppers, and other light-use products. High-density foams have densities ranging from 10 to 15 pounds and are ideal for applications that see heavy use, such as bedding, couch cushions, booth seating, or automobile seating.
Because density is measured by weighing a cubic foot of foam, people sometimes use the terms “weight” and “density” interchangeably. For this reason, you should be cautious of confusing foam’s density (or material) weight (the weight of a cubic foot sample) with its overall weight (the weight of the entire piece of foam).
Both figures are important, but each gives you different information.
The firmness of foam describes how it feels and reacts to pressure and weight. It is measured through mechanical performance testing and expressed in a unit called indentation load deflection (ILD) or indentation force deflection (IFD).
The testing uses a foam sample 15” by 15” by 4” in size and measures the force in pounds that is required to compress the material 25% (one inch) with a 50-square-inch circular indenter.
For example, if 40 pounds of pressure is necessary to compress the material one inch, the foam’s ILD is 40.
Testing results will not be accurate if the sample does not have the appropriate dimensions, as the thickness of the material affects how much weight it can support.
Greater pressure is required to compress hard foams, and less to compress soft foams. ILD values between 8 and 70 are common for most foam materials, with values reaching 120 to 150 designating a very high firmness.
Remember that firmness doesn’t reflect foam’s quality — density does. Firmness illustrates how a material feels and gives you an idea of how it will support weight in a particular application.
In fact, firmness and density have no direct correlation. Foam has different kinds of chemical and structural compositions, so it’s possible for foam samples with lower densities to have a higher ILD (firmness) than samples with higher densities. Consider each metric separately to select foam that is your ideal in both density and firmness.
Open-Cell vs. Closed-Cell Foam
Another characteristic of foam is related to its cell structure. Foam can be either open-cell or closed-cell.
In open-cell foam, the walls of the cells are broken, which allows air to enter the tiny pockets in the material. This gives open-cell foam a sponge-like look and soft, cushiony feel. Open-cell foam also tends to be less dense and weigh less than closed-cell foam.
One thing to keep in mind is that because of the porous quality of open-cell foam, water and water vapor can easily penetrate it. However, open-cell foam resists mold growth and won’t shrink, crack, or wear down with use.
The cells in closed-cell foam are, as you might imagine, closed and not connected to one another, so no air can fill them. The gas bubbles that form when the foam is expanded and cured are then trapped within these cells, giving the foam excellent insulation capabilities.
Unlike open-cell foam, closed-cell foam is resistant to water and water vapor. This makes closed-cell foam a good choice for exterior applications; but most upholstery projects will want to utilize open-cell foam for its durability and softness.
Need Help Choosing the Right Foam?
If you’re still unsure of which foam to choose for your business’s or client’s upholstery project, give us a call. We’re happy to explain your options and make recommendations — for foam, fabric, and any other element of the upholstery process.