Joint Industry Foam Standards and Guidelines
ARM AND BACK FOAM PERFORMANCE STANDARDS AND GUIDELINES
Foam backs and arms add comfort and impart design freedom, beauty, and style to upholstered furniture. The "best" foam for a furniture manufacturer's application may be based on many factors - styling requirements, "feel" of the back or arm and economics. Upholstered furniture backs and arms are usually made of foam or fiber or a combination of the two. While the seat is the support portion of the furniture and is usually judged on a strict durability criteria, backs, and to a lesser extent, arms, are the cushioning comfort components of furniture, with resiliency a less significant factor than seat foams.
This section is meant to give practical guidelines and ranges on back and arm foams in the daily manufacturing environment. Testing was carried out in an accurate and scientific manner. Test material was obtained from various foam suppliers out of daily production runs, so as to simulate the foam that is seen daily in the furniture manufacturing plant. While these are working guidelines for the industry in general, manufacturer and supplier relationships can supersede any of these guidelines if so agreed upon. Also , it should be noted that laboratory to laboratory variations can be present and must be resolved between testing facilities if a dispute should arise.
As a result of environmental legislation, low density back foams may have changes in physical properties in the future or could be eliminated altogether. A move to higher density, soft foams could happen as environmental concerns continue.
13.2 Test Methodology
The back foam committee was comprised of furniture manufacturers and suppliers and utilized up to six laboratory facilities. All tests performed on the back foams tested followed the guidelines of ASTM 3574, except for the dynamic fatigue test. Following is a list of the foam types tested and analyzed by the committee:
13.2.1 Test Samples
Foam test samples were cut from production runs of foam. A total of six samples were cut, top, middle, bottom, left and right. Samples were taken 8" from the top skin, 8" from the bottom skin, a minimum of 4" from the bun sides, and 4" from the forward and rear skin. Samples size was 30" x 24" and was divided into pieces for IFD/Hysteresis testing, CFD, Humid Aging and Compression Set testing.
In common foam terminology, nominal density names of foam refer to the top end of a density grade range. Upon laboratory testing of the foam samples, the following recommendations can be made concerning density: The range on all back and arm foams up to a 2 pound density should be minus 0.1 pound, plus 0.0. Filled foams such as melamines may sometimes be expressed as minimum densities.
13.4 IFD Ranges
IFD testing data on back and arm foam leads to the following conclusions: There are natural IFD spreads within a bun of foam. The middle of a bun, where it is hotter, produces the firmest foam within the block. The top, where it cools the quickest, is normally the softest. IFD ranges shipped to the furniture manufacturer should fall within +/- three pounds, unless density sorting arrangements have been made between the manufacturer and supplier. Although the ASTM IFD testing procedure is a precise machine test, there can be subtle differences between test machinery and laboratory test procedures that can show up as much as a 10% variation in IFD readings between labs.
Because of the sample size of 24"x24"x4", IFD ranges obtained in this round robin testing were higher than the standard foam industry grading procedures using a 15"x15"x4" sample size. For example, a foam grade of 1115 would test 1121 on the larger sample. However, all test results within the particular sample size showed the proper ranges of IFD correlation. It should also be noted that a larger piece of foam also produces a higher modulus value.
13.5 CFD versus IFD
Both IFD and CFD are compression force of deflection tests. The correlation shown between the two types of testing was that a grade of foam measuring firm on IFD would have a range of firmness on the CFD apparatus.
Test results show that most higher density foams have better hysteresis than lower density foam.
Many fatigue tests are available for testing purposes. This committee chose the constant force deflection flex fatigue test. The apparatus must be capable of deflecting the test specimens 75% of their original thickness with minimum distortion at a rate of 30 cycles/minute (+/- 5). Many labs did not have the capacity to test at cycles more than 30 cycles per minute, thus 50 cycles/ minute was not used. Sample size for CFD testing was 4"x4"x3". The initial thickness and 50% CFD values were determined using ASTM D-3574 Test C. After 100,000 cycles of flexing at 75% deflection, the specimens were removed and allowed to equilibrate for 30 minutes. The thickness and the 50% CFD value was measured for a second time. The change between the initial and final values was calculated to obtain the fatigue factor.
Test results from the CFD dynamic fatigue tests showed that back foams should perform well in all categories of density for back and arm foam requirements. However, no actual full scale furniture tests were run to correlate actual performance to the laboratory fatigue tests. [Higher density foams will have better fatigue properties and durability over the lower density foams, but the cost effectiveness of higher performance foams is often a major consideration of furniture manufacturers.]
13.8 Compression Set
Good consistency between laboratories. Compression set of less than 10% are acceptable for conventional back foams. HR and melamine foams will perform well with compression sets of up to 25%.