Literature

Joint Industry Foam Standards and Guidelines

SECTION 0.0

Published: 7/94

INTRODUCTION TO THE PHYSICAL PROPERTIES OF FLEXIBLE POLYURETHANE FOAMS FOR FURNITURE APPLICATIONS

0.1 Selecting the best foam for the intended end-use is a difficult and complex process; selecting the best foam for the desired comfort is even more difficult and complex; and, finally, selecting a foam that will be durable in use is also a complex process.

0.2 One of the reasons for the difficulties and complexities is economics. The best foam for the intended use may be too expensive for things like margin requirements and other pricing and cost ramifications.

0.3 Far too often, the determination of best foam for a particular job will be based on subjective interpretation of test results--vis-a-vis-opinions; because some of the test methods and their accuracies and reproducibilities simply leave the circumstance open to subjective opinion. Testing of certain physical properties of foams also is not very reproducible from lab to lab or machine to machine. Errors of 10 to 30 percent can exist in certain test procedures, and many of these errors are the result of poor test-experiment planning or communication. For example, IFD interlab testing often always leads to very wide differences in results; CD (compression deflection) testing often leads to wide differences in results; and flex fatigue testing also usually leads to very wide differences in test results.

NOTE: Because of the potential wide differences in test results, it is imperative that furniture manufacturers work closely and continuously with their foam suppliers to correlate equipment, procedures, and test data. Supplier/furniture manufacturer IFD correlation is very possible and even very practical if everyone involved is diligent in continual attempts to correlate and communicate.

0.4 The subject of comfort is extremely subjective and open to opinion. As a result, putting numbers on entities associated with comfort becomes very difficult. It must be realized that comfort is related to a composite-of-factors in a piece of upholstered furniture. Some of these factors are:

-SEAT DEPTH -SEAT-TO-BACK RATIO OF FIRMNESS
-SEAT HEIGHT -DEPTH AND TYPE OF BACK
-SEAT PITCH -KIDNEY ROLL SIZE (IF ANY)
-SEAT CUSHION FOAM USED -UNDER CONSTRUCTION OF BACK
-TYPE OF FABRIC USED -UNDER CONSTRUCTION OF SEAT
-CUSHION STUFFING RATIO -SPRING TYPE AND SPACING
-SEAT-TO-BACK ANGLE (PITCH) -SPRING CROWN HEIGHT
-TYPE AND AMOUNT OF CUSHION WRAP USED -USE OT HINGE-LINKS

 

0.5 The key point is that the foam alone is not the only factor determining the comfort of a seat. As a matter of fact, the foam is not even the greatest factor in the determination of seating comfort. Many of these factors listed above contribute and/or detract as much as does the type of seat foam used.

0.6 There is also another term related to comfort which is generally misused and causes some confusion. That term is "support factor". A much more acceptable term for the ratio of the 65% IFD to the 25% IFD is "modulus" or "compression modulus".

0.7 Cushion or seat complaints from the field usually arrive with comments like: "this seat has collapsed", "it's too soft", "the foam in this cushion is too soft", "these cushions are too mushy", "or the foam in these cushions is too hard". One can't blame the customer or the dealer for such comments, because the customer or dealer is usually quoting what they feel is obvious. It is up to the furniture manufacturer to thoroughly investigate all of the potential causes of the complaints and to technically define those complaints. Then proper solutions can be derived.

0.8 The question of in-use durability is difficult and complex, but it is still not impossible. There are many questions and differences of opinions as to which of the physical properties predict in-use performance. There are also many questions and differences of opinions as to how to test for the durability properties; but even with these questions and differences, there remains some good, common-sense, technically-based methodology for choosing good, durable foams.

0.9 More often than not, it is the lot-to-lot variation in a particular physical property that causes problems. For example, the absolute value of tensile strength above 8 p.s.i. bears little relationship to how a particular foam might perform in use or in the plant; but a lot-to-lot change in tensile strength of say 15-20% could be a harbinger of serious problems in the plant or in the field.

0.9.1 International environmental regulators have brought about the need to reformulate many polyurethane foam formulations. This reformulation has the potential to affect some of the physical properties of foams, such as hysteresis and flex fatigue. At this time, the total effects of the reformulation are not known.

0.9.2 It is the hope of The Joint Industry Foam Standards And Guidelines Committee that this standards and guidelines publication will greatly assist the furniture manufacturer and foam manufacturer to make sensible, prudent, and technically sound selections of polyurethane foams for all furniture applications.