August 1, 2025
Foam Production
Foam properties can be better understood with a little back- ground in how FPF is made.Flexible polyurethane foam is produced from a reaction of two key chemicals,a polyol and an isocyanate with water.These are mixed together in specific amounts with other ingredients,and the foam reac- tion begins almost immediately.Bubbles are formed,and the mixture expands.It's been compared to bread rising.In a matter of minutes,the reaction is complete.
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Slabstock Foam Process 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.Sides on the conveyor allow the foam to rise into a bun or slab anywhere from two to four feet high.The continuous slab is allowed to cure for typically 24 hours(longer for specialty grades).This manufacturing procedure is the slabstock produc- tion process. The cured foam is subsequently fabricated into useful shapes.Most foams for use in furni- ture and bedding are produced this way. |
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Molded Foam Process A second method,foam molding, is a process where individual items are produced by pouring chemi- cals into specially shaped molds and allowing the foam reaction to take place.Examples of uses include automotive seating,contract furniture,and pillows. |
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Raw Material Mixture The foam production process can be controlled through changes in the foam raw material mix.In addi- tion to the polyol,isocyanate and water used to produce foam,a variety of other chemicals and additives may be included based on customer specifications to change the final properties of the foam.These include: Auxiliary blowing agents,which augment the primary blowing agent(carbon dioxide),can be used to make foam softer or lighter;Catalysts, which control the speed of the reaction to improve productivity or change foam properties;Surfactants, which aid in the formation of foam cells; Flame retardant additives,used to improve a foam's resistance to ignition or burning.(Unfortunately,these tend to have a negative influence on the comfort,support,and durability of the foam.); Fillers, which increase the weight of the foam,but can possibly have a negative influence on the physical properties of the foam.By adjusting the chemical mix of the foam,foam producers can manufacture literally hundreds of different grades of foam,each with its own performance properties. |
Properties that Affect Foam Performance There are a number of physical properties of flexible polyurethane foam that guide the selection of FPF for different applications.Following is a brief description of key physical properties of foam,and the importance of each.Physical properties of foam are measured in a laboratory under closely controlled conditions of humidity and temperature.Care must be taken to reproduce those conditions when testing samples for physical properties. |
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Density Density is a measurement of the mass per unit volume.Measured and ex- pressed in pounds per cubic foot(pcf)or kilograms per cubic meter(kg/m3),density is one of the most important of all foam properties.Density is a function of the chemistry used to produce the foam and additives includ- ed with the foam chemistry.(Additives are sometimes used to give foam specialized properties.For example,gel additives to viscoelastic,or “memory”foam used in mattresses may be used to help users sleep cooler.) Density affects foam durability and support.Typically,the higher the density,the better the foam will retain its original properties and provide the support and comfort it was originally designed to produce. |
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IFD Indentation Force Deflection(IFD)is a measurement of foam firm-ness.Firmness is independent of foam density,although it is often thought that higher density foams are firmer.It is possible to have high density foams that are soft—or low density foams that are firm,depending on the IFD.IFD specification relates to comfort.It is a measurement of the surface feel of the foam.It is measured by indenting the foam 25%of its original height.Foams are typically offered in IFD ranges of±10%. |
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Support Factor A second IFD measurement is sometimes taken by indenting the foam 65 percent of its original height.This second IFD measurement is used to help determine the ability of the foam to provide deep down support. Typically,the more difference between the 25 percent IFD and the 65 percent IFD,the more ability the foam has to support weight.The ratio of the 65 percent IFD divided by the 25 percent IFD is called the foam's support factor. Support factors for foam range from about 1.5 to 2.6.The higher the number,the better the ability of the foam to provide support. Foams with high support factors offer a number of advantages.A low 25 percent IFD on a foam with a high support factor to create extra surface softness without causing the foam to "bottom out"when weight is applied. Typically,the higher the foam density,the better the support factor. |
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Dynamic Fatigue There are several tests that are used to determine foam durability,or how well foam retains its original firmness properties and height.Some are standard laboratory tests;others are customized tests developed by differ- ent manufacturers.But virtually allof them are based on flexing or com- pressing the foam a specific number of times to a set deflection or weight load,and measuring foam firmness and height before and after testing. Differences are called fatigue. In fatigue testing.foam samples may be compressed a few thousand times,or many thousands of times.The percentage ofIFD loss is then measured.Shorter tests provide an idea of how much firmness a foam may lose through initial use,while longer tests provide data on overall foam durability. |
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Roller Shear A particularly severe flex fatigue test is roller shear,where a rolling weight is run over a foam sample from two directions,typically for about 25,000 cycles.This roller shear test provides a combination of compression and abrasion,and helps identify how the foam would stand up to particularly difficult applications,such as commercial furnishings or as carpet cushion. Again,IFD loss is measured,and multiple measurements may be taken, at different time periods after the foam has had a chance to "recover." |
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Tear Strength Flexible polyurethane foams are also measured for their ability to resist tearing,breaking,or stretching.This is important in applications where foams must be handled frequently,such as in upholstering.The tests to determine these properties are tensile strength,tear resistance,and elon- gation.They determine the foam's ability to be stretched or flexed with- out tearing.These durability measurements are particularly important for foams which contain large amounts of fillers(such as combustion modi- fied foams),because these additives may increase the tendency of foams to tear or shred.When specifying foams that contain additives,tensile strength,tear and elongation tests should be reviewed to see if the foam may require special handling |
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Resilience(Ball Rebound) Resilience is an indicator of the surface elasticity or“"springiness"of foam.Resilience can relate to comfort.Resilience is typically measured by dropping a steel ball onto the foam cushion and measuring how high the ball rebounds.Foam resilience ranges from about 20 percent ball rebound to as high as 80 percent rebound.Higher resilience in a foam often means that sofa seat cushions,for example,have a better“hand”or surface feel. Foams can also be made to have very low resilience for certain applica- tions.For example,viscoelastic(memory foam)products typically exhibit very low resilience. |
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Hysteresis Hysteresis is another laboratory test used to determine a foam's ability to retain its original firmness properties. Hysteresis is measured by first indenting the foam sample 25 percent and measuring firmness,then indenting it 65 percent and again measur- ing firmness,and finally releasing indentation to the 25 percent level without allowing the foam to completely relax.Without fully releasing indentation,foam won't immediately recover all of its original 25 percent firmness,but the percentage of firmness it does recover is believed to be a good indicator of overall cushion durability. Unlike other durability tests,Hysteresis can be performed quickly on a variety of foam samples. |
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Testing Methods To learn more about testing flexible polyurethane foam,refer to ASTM International's test method,D3574,Standard Test Methods for Flexible Cellular Materials—Slab,Bonded,and Molded Urethane Foams,which details test procedures and terminology. |
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Air Flow Air flow is an important diagnostic test.Foam performance is optimized when air flow is maximized.This indicates that cells are open and as flexible as they should be.A good rule of thumb for air flow in flexible polyurethane foams is a minimum of 2.0 cubic feet per minute(cfm). (Note:Viscoelastic or memory foams have lower air flow because of their chemistry,but still perform as intended.) |