Good quality spring-down cushions cost about 30% more than a 1.8 density HR (High resilience) foam cushion of equal thickness.

In my experience the Spring-down cushions have been slightly more durable than the 1.8 density HR foam.

However, I have also found that a 2.5 density HR foam (which costs about the same as the Spring-down) is significantly more durable.

Note - Most people equate foam "density" with "firmness." They are not the same.

Density refers to the amount of foam in the cushion. For example a 2.5 density cushion is about 1/3 heavier than the same size cushion made of 1.8 density foam. Higher density foams will take longer to "break down" and are more durable.

Firmness is rated separately and based on other factors so that it is entirely possible to have a very firm 1.8 density foam or a very soft 2.5 density foam.

The biggest problem with a spring unit/pocket coil, or sometimes referred to as a marshall unit, is not so much the spring itself, but is the 1" or so thick foam that encases the spring unit. This 1" or less of foam sometimes just soft polyester fiber that covers the unit on top/bottom is what breaks down first, as its usually not of a high density type foam. This foam on both sides equal to 2" of seating support that once it breaks down and along with the normal softening of the polyester fiber or down/fiber blend wrap, makes the spring cushion a less durable cushion compared to a high density HR foam cushion.
If the spring unit is made from a larger stiffer wire, with either a very high density foam topper or a high density polyester pad then the spring unit will outlast a HR foam of same thickness.

rmanbike - Good analysis.

The problem from the consumer's point of view is that there is virtually no way to determine what quality, density or thickness of the foam/fiber/down/feather wrapping and padding is being used to encase a specific spring unit.

rmanbike- but even if the 1" cushion breaks down, the coils themselves can still be good and still provide good support, can they not? I think of inner spring mattresses that use marshall coils, but may only have an inch of padding on either side. This structure on a mattress can last 8-10 years despite break down of the foam padding which does not last as long. Do you have experience with the spring cushions actually failing prematurely? Not trying to be argumentative, but trying to understand all the facets. Leggett and Platt's assertion is that their version of the cushion does not fail nearly as fast as standard 1.8 high density foam (which is often quoted as only a five year life). Does a company like leggett and platt also provide the desired foam specs to sofa manufacturers or do they only provide the coil units themselves and let the manufacturer choose to case them however they want?

Can a consumer tell anything by unzipping the cushion and seeing the foam layers on the cushion. Maybe they can't tell what the density of the foam is, but can they tell whether there are more layers besides just a layer of polyester batting.

Depends entirely on the quality, IMO.

Can't post the photos right now, but I've repaired a lot of both under warranty.

SirJohn, I think sitting on a cushion that's 5" thick which also concentrates almost all your weight into a small area, compared to lying down on a mattress that is 10" thick, is why you cant really compare, not apples to apples!

Legget & Platt is a component manufacturer and as far as I know they arent in the business as sofa cushion fabricator.

If your concerned about the quality of a manufacturers cushions, I suggest calling them and asking for this information. A manufacturer with excellent customer service will provide this info, it may take several days or longer to have this information.

Foam needs to have a fire retardant applied. Many fire retardants are carcinogenic. So these spring units might be the way to go.

A down wrapped coil cushion with a high quality foam such as Ultracel will in my opinion outlast any cushion on the market. I also feel these cushions are also the most comfortable. This is how the cushion is constructed. To begin with your average size cushion should have about 75 coil springs encased in fabric. The springs are then encased in some sort of fiber. This is then surrounded by foam and as I said preferable a quality foam such as Ultracel. It is then wrapped in in a mix of 50% fiber 50% down and feathers. This down and feather mix is usually about 90% to 10% or 80% 20% (down to feathers). You can order any mix you want but this is typical. I would describe how this cushions sit is like going down in an elevator sinking through the layers. When you stand up the cushion resumes it shape and thus the cushions are less wrinkly.

Does anyone know of a company willing to ship a replacement coil set to Canada? All I need to do is repair one cushion.