What is the difference between a sofa cushion's foam density and firmness?
Wednesday, February 28, 2018
[The Insider's Guide to Furniture blog contains over 500 articles, including new articles published after March, 2022 and updates of articles in this blog.]
Although most people think that a cushion's foam density and firmness are synonymous, they are actually very different.
The density of foam is found by weighing a 12″ x 12″ x 12″ block of the material. If a product has a 2 lb. density, that means a 12″ x 12″ x 12″ foam block weighed 2 lbs.
Although density does not pertain to the firmness of a foam cushion, it does correlate to the quality and longevity of that cushion.
Each foam density is available in a wide variety of different firmnesses.
Most foam suppliers typically stock four or five commonly used densities for residential furniture seat cushions ranging from 1.5 to 2.5. The number designates the weight (in pounds) of 1 cubic ft. of foam.
Each of these different densities may be available in 10 or more different firmnesses ranging from very soft to very firm.
Cushion construction is the single most important factor in determining the lifespan (and comfort) of your sofa, couch or chair.
The expected lifespan of a foam cushion is primarily dependent on the density and thickness of the foam.
Another important factor is whether the foam is HR (High Resiliency) which recovers its shape better after use.
A foam cushion's "firmness" has very little effect on the expected lifespan.
Since most consumers equate “firmness” with durability, cheap foams are often made “extra firm.” With a low density foam, however, that “extra firm” feeling will not last long.
Foams used in seat cushions for moderately priced residential furniture generally range from 1.5 through 2.0.
The most common foam density by far for residential seating is 1.8. Depending on the thickness of the foam, whether or not it is HR (High Resilience) and how much use the couch gets, a 1.8 density cushion will typically begin to lose its shape and resilience in 1–3 years.
After 3–5 years a 1.8 density cushion will normally need to be replaced. Few retailers or manufacturers offer replacement cushion inserts.
Since replacing cushions is not simple or cheap many people choose to purchase another sofa when their cushions wear out.
Replacing worn out cushion insides requires going to a professional upholsterer (or re-upholster.) The cost for purchasing a new set of custom cushions can get very expensive.
The result is that many consumers choose to purchase a new sofa when their cushions wear out, even though the frame, foundation and even the fabric may still be in excellent condition.
Lower density foams are typically used for back cushions or padding that goes over the arms or other parts of the frame.
Higher densities (2.0 - 2.5) can be found on more expensive residential furniture.
Furniture designed for heavy commercial or institutional use may use foam with densities of 3.0 or higher.
The higher the foam density the more the cushion will cost. Variations in firmness usually do not affect cost. HR (High Resiliency) foam is more expensive (and more durable) than non-HR foams.
The most commonly used foam density for residential furniture sold in the U.S. is 1.8.
The term "High Density Foam" is almost meaningless. It is used in marketing materials to describe virtually any foam from 1.8 density and up.
The foam core is usually anywhere from 4″ - 6″ thick and is typically wrapped in a dacron polyester fiber. The wrapping may consist of a layer of memory foam in place of the dacron polyester.
The fiber (or memory foam) wrapping is generally 0.5 - 1.5" thick on the top and bottom of the cushion. It softens the feel of the cushion but has no effect on lifespan.
A 4" thick foam core made with 1.8 density HR (High Resiliency) foam can be expected to last about 2 years with average use before the foam begins to lose its ability to bounce back and keep its shape .
A 5" thick foam core made with 1.8 density HR (High Resiliency) foam can be expected to last about 3 years with average use before the foam begins to lose its ability to bounce back and keep its shape.
Foam cushions will typically still be usable for another couple of years after the deterioration process begins. Foams that are not High Resiliency will deteriorate more rapidly.
Actual foam densities will vary during the manufacturing process. A variation of 0.1 is considered normal. A 1.8 density foam may actually be 1.7 or 1.9. Larger variations are not unusual.
There are many couches sold with cheaper (and lighter weight) 1.5 density foam that will deteriorate even more rapidly, sometimes within one year of purchase.
The overall thickness of the cushion may or may not be an indication of a cushion’s durability.
“Value priced” couches will sometimes have cushions that are bulked up with several inches of polyester fiber around the foam core.
The excess polyester fiber will rapidly compress causing the cushion to lose its shape.
If you want to get more than 5 years of use from your couch you will need to find a couch with a better quality cushion.
Higher priced couches generally use thick higher density foams with at least a 2.0 density. but preferably higher.
More expensive cushions may also include coil spring construction, sometimes with a layer of down and feathers to give a long lasting cushion with a softer feel.
Plush cushions made exclusively with down and feathers used to be very popular in high end furniture long ago, but are rare now. Aside from the very high cost, down and feathers have very little resiliency and need to be "fluffed up" after each use.
When shopping for a couch always test the cushions by picking them up. As a general rule if the seat cushions feel “light” you are looking at a couch with a very short expected lifespan.