A great misconception exists about what defines "proper" seating comfort.

Designer: "I need a firm seat for a heavy-use contract application."

Consumer: "I need a sofa for my home that I can sink into."

So what do manufacturers do? Often, they supply a single slab of firm poly-urethane foam on a seat designed for contract application. Would you want the same type of foam on your guest seating or sofa at home? Probably not. For residential seating, many manufacturers simply supply a soft, low density slab (which lowers the cost) -- and may result in an overly soft and nonsupportive product.

What really determines "proper" seating comfort is an upholstered chair's intended use and how long people sit in it -- not whether it is for home or office.

Three Criteria
Many factors enter into seating comfort: seat height, seat depth, back pitch angle, seat pitch angle, ratio firmness of seat to back, "ride" (deflection), "cradling" (distribution of body weight on cushioned surfaces), spring and webbing types, basic frame design, as well as fabric and decking materials. Because some manufacturers do not always adequately study and prototype each new chair or sofa model before putting it on the market, specifiers should be clear on what definition of comfort and purpose best matches the upholstered seating they consider specifying or purchasing.

Even so, is it possible that seating can be made comfortable for all individual sizes, shapes and weights of the people who sit on it? Probably not, but certain factors can be controlled. Modern polyurethane foam universally used for seat and back cushions in all types of upholstered seating, whether contract or residential, is one of the most controllable factors that determines seated comfort -- and long-term customer satisfaction. Yet, polyurethane foam is one of the least understood seating components.

Although a number of different criteria may be used to select the proper types of polyurethane foam for a given product and application, virtually every selection includes the following three elements:

• Support -- The foam has to be able to support the proper amount of body weight in order to properly cushion the sitter.

Whenever the cushion (especially the seat) is thick, you generally want to have it "give" easily as you first sit, then become firmer as your entire weight is on the chair. The support factor of foam is measured by dividing the pounds of firmness, or Indentation Force Deflection (IFD), needed to compress the foam to 65 percent of original height, by the IFD required to compress the foam to 25 percent of original height. The higher this ratio the better the "deep down" support to the sitter.

In Europe, quality manufacturers of upholstered contract and residential seating obtain high support factors by laminating softer (low IFD) foams on top of firmer (high IFD) foams. This yields a pleasing initial softness to a chair, but with lasting firm support for the human body over many hours. This lamination, or multidensity process, is not as common in the United States as it is in Europe -- which is why you usually get just a firm seat for contract or a soft one for residential use, with no consideration of the support factor and its relation to genuine seating comfort.

• Density -- Is the weight of a cubic foot of foam, not to be mistaken for firmness as measured by IFD. In fact, the density of foam is independent of its firmness, low density foam can be made firm and vice versa. The higher the foam density, the greater its support, its durability and its cost. Since density cannot be measured by looking at a foam cushion, general "feel," cradling and support provide useful indications. You should investigate the density of foam in all products because low density foam can be found in products at all price points.
• Durability -- The foam has to hold up through years of continuous use without excessive loss of its dimensions and original properties. Higher foam density yields greater durability.

These are the basic benefits that polyurethane foam cushioning provides. By evaluating each of these three areas first, selecting a chair with proper foam for a given use, or specifying an upgraded foam for particular seating applications, becomes fairly simple. Seat cushions on sofas, for example, must have good support, comfort and durability, while arm and back cushions for the same sofa need to last and be comfortable -- but are not necessarily required to support much weight.

Manufacturing Foam for Cushions
Flexible polyurethane foam is produced from a reaction of two key chemicals, a polyol and an isocyanate. Today's polyurethane is CFC-free. The chemicals are mixed together and poured in very specific amounts with specialized pumps and with other ingredients. The foam reaction process begins almost immediately. Bubbles are formed and the mixture expands. In mere minutes, the reaction is complete.

To manufacture foam for cushioning, two basic procedures are used. In one, the chemical mix is poured onto a moving conveyor, where it is allowed to react and expand. Slides on the conveyor allow the foam to rise into a "bun" or slab anywhere from two or four feet high. Each "bun," or product, has its own formula for various specifications of density, firmness, etc.

The continuous slab is then cut, stored and allowed to cure for up to 24 hours. This manufacturing procedure is the slabstock production process. Once cured, slabstock foam can be cut to shape and fastened to chair frames. Most foams for use in furniture, particularly residential furniture, are produced this way.

A second method, foam molding, is a process where individual items are produced by pouring foam chemicals into specially shaped molds and allowing the foam reaction to take place. Some contract furniture manufacturers use foam molding for seat and back cushions. Molded foam allows a range of curved shapes and higher resiliency where adding layers of foam is not feasible.

As with any product specification or substantial purchase, it pays to ask questions. Understand how the manufacturer of sofas, lounge and operational seating normally constructs its product -- and what construction options are available. Most manufacturers have a stake in doing business with you and your firm again. Make sure they know how the intended product is to be used (e.g. one versus two shifts a day; by one identifiable person or by a number of different people; if there is a projected practical lifespan for the products, such as five years or 10 years).

Selecting seating is a bit like selecting cars. They all look good in the showroom. But when you ask questions, and understand how each manufacturer makes its product, hidden yet meaningful differences become known.

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