Question:
What is the difference between foam density and firmness?
Do extra-firm cushions last longer than less firm cushions?
Answer:
Foam density and firmness are very different things when discussing cushions.
Cushions are measured by two values:
The density or weight per cubic foot of polyurethane foam. The higher the number the more it weighs.
Foam that has a density of 1.8 contains 1.8 lbs of foam per cubic foot.
For cushions, the term, “High Density” can refer to any foam that is 1.8 density or higher.
When a website, salesperson, or ad states that cushions are “high density” without a number, you can safely assume that the cushion’s density is 1.8.
Firmness is measured by the foam’s IFD (Indentation Force Deflection) number.
The IFD number tells you how much weight it takes to compress the foam by one third. Lower IFDs mean softer cushions. Higher IFDs are firmer.
For residential seating, IFD numbers for medium firm generally range from 32 – 38. Extra-firm may have IFDs of 40 – 50.
Commercial and Institutional seating, with thin heavy-duty cushions, may have IFDs ranging close to 80 or 90.
The most common foam, by far, used for seat cushions is 1836, which means a 1.8 density foam with a medium-firm IFD of 36.
Density has a direct relationship with how long a foam cushion will last.
Firmness does not affect a cushion’s lifespan.
Density does not change over the entire lifespan of the cushion.
A cushion’s firmness decreases over time.
Higher density foams weigh more than lower density foams.
If you are uncertain of a cushion’s foam density, pick it up.
Lightweight seat cushions will not last very long.
The heavier a cushion is, the longer it will last.
Different types of foams have different density scales.
Seat cushions are usually made from polyurethane foam. The most common density is 1.8
Memory and latex foams are denser.
Although these foams are sometimes found in seat cushions, they have far higher densities.
A 1.8 density memory or latex foam cushions would not be suitable in a seat cushion.
It is not unusual to see see cushions described as “memory foam.”
In almost all cases, this refers to a thin 1 or 2 inch thick strip of memory foam glued on top of a polyurethane foam core.
The purpose of the memory foam is to soften the feel of the polyurethane foam core.
Latex foam cushions are sometimes found in high end seating.
Latex foam is recyclable and bio-degradeable. It is mold, mildew and mite-resistant and is not flammable.
This foam is easily identifiable. Latex cushions are much heavier than similar size cushions made from polyurethane.
Latex is more durable and far more expensive than polyurethane.
Cushion construction is the single most important factor in determining the lifespan (and comfort) of your sofa, couch or chair.
Cushions are usually the first part of low and mid-priced sofas to wear out.
The expected lifespan of a foam cushion is primarily dependent on the density, thickness, and surface area of the foam core.
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 lower 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.
1.8 density cushions often need replacement within 3 – 5 years, but many people will continue to use their couches long after they have lost their initial comfort.
Few retailers or manufacturers offer replacement cushion inserts for their low and mid-range seating.
The cost of replacement cushion cores is higher than most people are willing to pay for their low and mid-priced sofas.
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-upholstery shop.)
Depending on the quality and size, the cost for replacing a polyurethane foam seat cushion core can be anywhere from $100 – $250 per cushion.
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 (2.4 – 2.8) are usually found only on more expensive high end residential furniture.
Furniture designed for heavy commercial or institutional use may use foam with densities of 3.0 or higher.
Foam cushion cores for residential seating are usually anywhere from 4″ – 6″ thick and 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.
Foam’s thickness* and total surface area also affect cushion 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.
Cushions with larger surface areas last longer because they spread out the sitter’s weight and lower the lbs. per sq. inch of pressure exerted on the foam.
2 cushion sofas should last longer than the same size 3 seat sofas using similar foam.
*The cushion’s overall thickness is not as important as the foam thickness.
A cushion with a 6″ thick foam core and a 6″ overall thickness will last longer than a cushion with an 8″ overall thickness, resulting from a 5″ thick foam core + 3″ of dacron fiber wrapping.
Foams that are not “High Resiliency” will deteriorate more rapidly.
Since the process that adds “high resiliency” is not expensive (adding about $1) most seat cushions are made with high resiliency foam.
Although “high density” and “high resiliency” have two very different meanings, the terms are very often used interchangeably by salespeople, and home furnishings websites.
Actual foam densities will vary during the manufacturing process.
Polyurethane foam is poured into huge blocks that measure 12 ft. x 4 ft. wide x 8 ft. high.
These large blocks of foam will vary in density from one part of the block to another.
A density variation of 0.1 is considered normal, but larger variations are common.
The best quality foams, such as Qualux or Ultracel, will have very little variation.
Lower quality foams may have far more variation.
In general, polyurethane foams made in Asia are lower quality than those made in the USA.
Several years ago, I suspected that my cushion supplier was not sending my company the 2.5 density foam we specified.
A dozen cushions from 6 different shipments were sent to an independent laboratory to test the foam densities.
Results from the testing showed that out of the dozen samples tested, only half were within the acceptable 2.4 to 2.5 density range.
4 samples tested at 1.7 to 1.9 and two others at 2.1 & 2.2
At that point, we started making our own cushions, rather than buy them from an outside supplier.
The overall thickness of the cushion may not be an indication of a cushion’s durability.
“Value priced” couches will sometimes have cushions bulked up with several inches of dacron polyester fiber wrapped around the foam core.
The excess fiber soon compresses, causing the cushion to lose its shape.
If you want to get more than 5 years of use from your couch, you will need better quality cushions.
High quality brands may offer 1.8 density foam on their standard cushions, but they will always have cushion upgrade options.
Upgrade options may include higher density foams.
Spring Down or Spring fiber cushions last 15+ years for most people.
Spring down cushions and foam cushions with a down/feather top layer usually use 5% down/95% feathers or 10% down/90% feathers.
The small amount of down used in these upgrades adds only a few dollars to the cushion’s cost as compared with polyester fiber.
Down and feather cushions are very soft and very expensive. The softness and cost are determined by the amount of down used.
Cushions made with 50% down & 50% feathers can cost hundreds of dollars more than cushions made with 10% down & 90% feathers.
Down and feather cushions have very little resiliency and need to be “fluffed up” after each use.
When shopping for a couch and you do not know the foam density, you can still estimate a cushion’s durability from its weight.
Pick up a cushion. If it feels “light,” it will not last very long.
Most cushions will feel about the same. Those are probably 1.8 density.
If a cushion feels heavier, it should last longer.
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