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.

Cushions are measured by two values:

Density

Cushion density is the weight per cubic foot of polyurethane foam.

The higher the number the more it weighs per cubic ft.

Foam that has a density of 1.8 contains 1.8 lbs of foam per cubic foot.

This is the most common density of foam used for seat cushions.

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” or “high resiliency” without a number, you can assume that the cushion’s density is 1.8.

Firmness

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.

Foam Density does not change over time.

If your seat cushions are 1.8 density when new, they will still be 1.8 density 5 years later when they are worn out.

For a specific cushion size, higher density foams will last longer than lower densities.

As foam density increases, the increase in durability can be substantial.

Foam Density is the most important factor that determines how long your cushions will last.

For example, an average size seat cushion for a three seat sofa might be 24 inches wide x 27 inches deep x 5 inches thick.

The average lifespan for this cushion, when used by a 160 lb. person would be:

1.8 density: 4 – 5 years

2.0 density: 6 – 7 years

2.2 density:  8 – 10 years

2.5 density: 15+ years

Increasing the surface area or thickness of the foam will also increase the average lifespan.

Increasing the weight of the people sitting on the cushions will decrease the average lifespan.

If we use the same foam densities, but increase the weight of the sitter to 250 lbs., the average cushion lifespan will change.

Now we have:

1.8 density: 1 – 3 years

2.0 density: 2 – 4 years

2.2 density:  4 – 6 years

2.5 density: 10 – 15 years

Foam densities of 2.5 or higher will lose less of their average lifespan as a person’s weight increases.

The best cushion for individuals weighing 250 lbs. or more is Spring Down.

Spring Down cushions will lose very little of their firmness or comfort when used by individuals weighing 250 to 300 lbs.

Foam Firmness changes over time.

The firmness begins to decrease from the first day you sit on your cushions.

The more you weigh or use the furniture, the faster the cushions break down.

A foam cushion is “worn out” when the foam firmness has decreased to the point where the cushion is no longer comfortable.

As shown above, higher density foams slow down this loss of firmness.

Cushions can be “too firm.”

Low cost seating is sometimes made with “extra-firm” cushions.

Extra-firm cushions may retain their shape longer than “softer” cushions.

But it will not slow the rate at which the cushions will collapse or the sofa will lose its comfort.

High Resilience cushions.

Resilience in foam is the ability to bounce back after a weight is removed.

The term “high resilience” generally refers to cushions that are not “extra-firm.”

But the exact measurement of how firm (or soft) a foam should be to be labelled “high resilience” is so vague that it’s almost meaningless.

In the mattress industry, “high density foam” usually refers to “extra-firm” foam that is at least 1.8 density.

Firm and medium-firm or softer polyurethane foams, used in mattresses, that are not “memory foam” are referred to as “high resilience” foams.

Memory foams are not “high resilience” since they do not “bounce back” quickly after weight is removed from them.

“High density” and “High resilience” have different definitions for foam used in sofa cushions.

For sofa cushions, the terms “high density” and “high  resiliency” are sometimes used interchangeably.

At other times, “High resiliency” may be used to describe softer foams that are not “high density.” For example, a 1.5 density foam should not be described as “high density,” but may be referred to as “high resilience.”

Foam fabricators (companies that manufacture the foam) have very strict (and complex) definitions and standards for which foams are “high density” and/or “high resiliency.” 

But furniture manufacturers, salespeople and other furniture industry professionals are far more casual about how these terms are used.

Marketing materials from furniture companies often use “high density” and “high resilience” to imply superior quality foam, but in reality cheap foams with low durability that can wear out within 3 years or less may be described as either “high density” or “high resilience.”

Loss of comfort is not always caused by the cushions losing their firmness.

The seat support foundation underneath the cushions also affects the firmness, comfort, and durability of the cushions.

For example:

Ashley recently changed its seat support foundation from sinuous wire springs to a wooden platform.

Their marketing materials claim the platform is more durable.

That may be true, but the hardness of the plywood platform top will break down the cushion foam faster.

As the foam breaks down, you will begin to feel that hard plywood board. It is not a comfortable type of firmness.

The same evolution to wood platforms occurred in the mattress industry, beginning about 50 years ago.

Prior to that time, most mattresses rested on box springs.

Switching to plywood platforms was much cheaper.

The mattress companies quickly discovered that to maintain comfort with a plywood box support, the mattresses had to be made much thicker (and more heavily padded.)

Some sofa manufacturers, trying to cut costs, have not yet recognized that when the spring (or webbed) foundations are removed, the cushions require more padding to maintain comfort.

Cushions used together with plywood platforms will quickly become uncomfortable and “used up” unless the foam density and/or thickness is increased.

Pocketed coil cushions are popping up in lower priced furniture.

Most of these are 4 inches thick and uncomfortably firm.

IKEA has successfully introduced 6 inch thick pocket coil cushions (with 3 inches of foam padding above the springs.)

Although these cushions are still firmer than normal, they are not uncomfortably firm for most people.

IKEA’s pocketed coil cushions will maintain their intial comfort and shape up to 10 years.

That’s twice as long as similarly priced sofas made with 1.8 density foam.

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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