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Sponge test
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Sponge performance
Flexible polyurethane foam is produced by reacting a polyol blend (including catalysts, surfactants, foaming agents, and cell-opening agents, among others) with TDI or MDI isocyanates. After curing, the foam can be cut into pieces and used in a wide range of applications. These foams are commonly used in furniture, bedding, and automotive applications to manufacture seats and mattresses, improving ergonomic comfort. High-performance and rigid foams are also used as structural materials for weight reduction in the automotive and aerospace industries.
To gain a comprehensive understanding of the mechanical properties of materials and meet the diverse requirements of foam products, extensive foam testing is essential. The following are some common test standards for polyurethane foams.
◉ ASTM D3574 - Flexible Cellular Materials - Slabstock, Bonded, and Molded Polyurethane Foams
◉ ASTM D3575 - Standard Test Methods for Flexible Cellular Materials Made from Olefin Polymers
◉ ASTM D3576 - Standard Test Method for Cell Size in Rigid Cellular Plastics
◉ ASTM D348 - Standard Test Methods for Microporous Polyurethane Materials
◉ ASTM D3453 - Standard Specification for Flexible Cellular Materials - Polyurethane for Furniture and Automotive Cushions, Bedding, and Similar Applications
◉ ASTM D3768 - Standard Test Methods for Microporous Polyurethane - Bend Recovery
◉ ASTM D3768 - Standard Test Methods for Microporous Polyurethane - Sagging Under High Temperatures
◉ ISO 2439 - Flexible Porous Polymer Materials - Hardness Measurement
Among them, ASTM D3574 is widely used for performance testing of polyurethane foams and includes several test procedures:
|
ASTM D3574 |
Project Name ( English ) |
|
Test A |
Density |
|
Test B1 |
Indentation Force Deflection Test (IFD) – Specified Deflection |
|
Test B2 |
Indentation Residual Gauge Length Test (IRGL) - Specified Force |
|
Test C |
Compression Force Deflection Test |
|
Test D |
Constant Deflection Compression Set Test |
|
Test E |
Tensile Test |
|
Test F |
Tear Resistance Test |
|
Test G |
Air flow test |
|
Test H |
Resilience (Ball Rebound) Test |
|
Test I1 |
Static Force Loss Test at Constant Deflection |
|
Test I2 |
Dynamic Fatigue Test by Roller Shear at Constant Force |
|
Test I3 |
Dynamic Fatigue Test by Constant Force Pounding |
|
Test I4 |
Dynamic Fatigue Test for Carpet Cushion |
|
Test I5 |
Dynamic Fatigue Test by Constant Deflection |
|
Aging Test J |
Steam Autoclave Aging |
|
Aging Test K |
Dry Heat Aging |
|
Aging Test L |
Wet Heat Aging |
|
Test M |
Recovery Time |
|
Test N |
Hysteresis Loss |
Density - Test A
Density is the weight per unit volume, expressed as lb/ft³ (pcf). It is commonly expressed in grams per cubic centimeter (g/cm³) and can be converted to pounds per cubic foot (pcf) by multiplying by 62.4. Density can be determined from samples of any size. It is independent of cell size, meaning that both coarse-cell and fine-cell foams can have the same density.
In addition to ASTM D3574 Test A, the following standards are also available for foam density testing:
◉ ISO 845:2006
◉ JIS K6767:1999 Section 7.1 (Polyethylene foam plastics)
◉ GB/T 6343-2009
◉ ASTM D1622/D1622M-14 (Rigid foam)
◉ JIS K6401:2011 Section 6.3
Indentation Hardness - Indentation Force Deflection (IFD) - Test B1
IFD (also known as “ILD”) is a test method used to determine load-bearing capacity (firmness or stiffness). It is expressed as the force in pounds required to achieve a specific percentage of foam deflection using a 50 in² indenter.
For example, to obtain a 25% IFD value, a 50 in² circular indenter is pressed into a 15 in × 15 in × 4 in foam sample. When the deflection reaches 1 inch, corresponding to 25% compression of the 4-inch-thick sample, the test is stopped. The test apparatus records the force (lb) required to maintain the indentation after one minute. A higher force reading indicates greater foam load-bearing capacity.
In addition to ASTM D3574 Test B1, the following standards are also available for foam IFD testing:
◉ EN ISO 2439:2008 (Flexible materials)
◉ JIS K6400-2:2012 (Flexible materials)
◉ GB/T 10807-2006 (Flexible materials)
◉ ASTM D5672/D5672M-15 (Flexible materials)
Sag Factor
Sag Factor is the ratio of the 65% IFD value to the 25% IFD value, expressed as a numerical value with one decimal place. It provides an indication of cushioning quality. Sag Factor values are typically between 1 and 3. A higher value indicates better resistance to “bottoming out,” while a lower value indicates that the foam is more likely to bottom out.
Recovery Ratio
Recovery Ratio is the ratio of the released 25% IFD value to the initial 25% IFD value after measuring the 25% and 65% deflection IFD values, followed by releasing the foam back to 25% deflection. The recovery ratio is expressed as a percentage.
Guide Factor
Guide Factor is the ratio of 25% IFD to density, expressed as an integer. It is useful for determining the relative firmness of foams with different densities. It is also used to compare foam cost efficiency. A higher Guide Factor indicates a more economical foam, as a firmer foam can be achieved at a lower density.
Compression Force Deflection (CFD) - Test C
CLD is also a measure of firmness and is expressed in pounds per square inch (psi) at a specified deflection percentage. The sample size is 2 in × 2 in × 1 in thick. In this test, the entire sample is compressed under a 50 in² compression plate. The procedure is the same as IFD testing. Values at 25%R and 65%R are recorded. For foam materials, it is common practice to specify only the 25%R value.
Both IFD and CFD can be tested at 50%R or any other deflection point based on customer/supplier agreement.
Compression Set - Test D
Compression set measures the permanent deformation of foam after compression between two metal plates under controlled time and temperature conditions. The standard condition is 22 hours at 70°C (158°F), with the foam compressed to a specified percentage of its original thickness, typically 50%. Compression set is expressed as the percentage of original thickness retained after deformation. For example, if a 2 in × 2 in × 1 in sample measures 1.00 inch before compression and 0.95 inch after testing, the compression set value is 5%, meaning the foam has not recovered 5% of its original thickness.
In addition to ASTM D3574 Test D, the following standards are also available for compression set testing:
◉ EN ISO 1856:2018 (Flexible materials)
◉ GB/T 6669-2008 (Flexible materials)
◉ GB/T 10653-2001
◉ ASTM D3575-20 Suffix B
◉ ASTM D1056-14 Sections 50-56
Tensile Strength - Test E
Tensile strength measures the force required to stretch a foam sample with a cross-sectional area of 1/2 square inch until failure. It is expressed in pounds per square inch (psi). Tensile specimens are cut into a dumbbell shape, as shown below.
In addition to ASTM D3574 Test E, the following standards are also available for tensile strength testing:
◉ EN ISO 1798:2008 (Flexible materials)
◉ GB/T 10654-2001 (Flexible materials)
◉ JIS K6767:1999 (Polyethylene foam plastics)
◉ ASTM D3575-20 Suffix T
◉ GB/T 6344-2008 (Flexible materials)
◉ GB/T 24451-2009 Clause 7.9 (Slow-recovery flexible PU foam)
◉ GB/T 24451-2020 (Effective from February 1, 2021)
Tear Strength - Test F
Tear strength measures the force required to continue tearing a foam after the tear has started. It is expressed in pounds per linear inch (pli). Tear strength is an important property when foam is sewn or attached during application.
Left: Tensile Strength, Right: Tear Strength
In addition to ASTM D3574 Test F, the following standards are also available for tear strength testing:
◉ EN ISO 8067:2018 (Flexible materials)
◉ GB/T 10808-2006 (Flexible materials)
◉ JIS K6767:1999 (Polyethylene foam plastics)
Elongation
Elongation measures the extent to which foam can be stretched before breaking and is expressed as a percentage of its original length. Elongation can be measured during tensile strength testing.
The following standards include elongation test methods:
◉ ASTM D3759/D3759M-05(2019) Procedure A, C, D
◉ ASTM D1000-17 Sections 37-45
◉ GB/T 30776-2014 Method A
◉ GB/T 7753-1987 (Withdrawn)
◉ ISO 29864:2018 Method A
◉ EN 14410:2003 Method A (Withdrawn)
◉ JIS Z 0237:2009 Section 8
Bond Strength
Bond strength measures the force required to separate two substrates bonded together and is expressed in ounces.
Air Flow Test - Test G
The air flow test measures the ease with which air passes through a foam sample. The test places a flexible foam specimen in a chamber and creates a specified constant pressure difference. The airflow rate required to maintain this pressure difference is recorded as the air flow value.
To reduce the volume of sponge products, they are often compressed. However, the sponge should recover to its original height after release. Foams with low airflow recover more slowly after compression. Air flow testing helps prevent the production of closed-cell or overly compressed sponge materials.
Impact Resilience (Ball Rebound) - Test H
Impact resilience measures the elasticity, rebound performance, or resilience of foam and is expressed as the rebound percentage.
The sample size is 4 in × 4 in × 2 in.
To determine the rebound percentage, a 16.3 g, 5/8 in steel ball is dropped through a transparent plastic tube onto an 18 in foam sample. Marks are made at every 5% rebound level. Three drops are performed, and the average of the three readings represents the percentage of the original height recovered by the ball.
Ball Drop Rebound Testing Equipment
In addition to ASTM D3574 Test H, the following standards are also available for ball rebound testing:
◉ ISO 8307:2018 (Flexible materials)
◉ EN ISO 8307:2018 (Flexible materials)
◉ GB/T 10652-2001 (Polymeric cellular flexible materials)
◉ GB/T 6670-2008 (Flexible materials)
◉ Q/JLY J711185-2008 Clause 7.4
◉ QC/T 56-1993(2017) Section 6.2 (Automotive seat cushion materials)
Fatigue - Test I
Three types of fatigue tests are:
Static Fatigue: The 25% and 65% IFD values are measured first. The foam sample is then compressed to 75% of its original thickness and held for 22 hours, followed by a 30-minute recovery period. The 25% and 65% IFD values are measured again, and the loss of force is calculated.
Roller Shear Fatigue: A stainless-steel roller is used to apply dynamic fatigue to foam samples for 5 or 12 hours, with 8,000 or 20,000 cycles, respectively. The IFD values before and after fatigue are compared, and the percentage loss of load-bearing capacity is calculated.
Constant Force Impact Fatigue: A flat horizontal compression plate is used to apply fatigue testing to foam samples, with 8,000 cycles completed within 2 hours or 80,000 cycles within 19 hours. The 40% IFD values before and after fatigue are compared, and the percentage loss of load is calculated.
In addition to ASTM D3574 Test I, the following standards are also available for fatigue durability testing:
◉ EN ISO 3385:2014 (Flexible materials)
◉ GB/T 18941-2003 (Flexible materials)
◉ QB/T 2819-2006 (Flexible materials)
Steam Autoclave Aging - Test J
Steam autoclave aging treats foam samples in a steam autoclave and then retests specific physical properties to evaluate significant degradation under high-temperature and high-humidity conditions.
ASTM D3574 Test J specifies two conditions:
At 105 ± 3°C for 3 hours, and
At 125 ± 5°C for 5 hours.
Condition 1 is typically used for polyester foams, while Condition 2 is used for polyether foams.
Dry Heat Aging - Test K
Dry heat aging involves conditioning foam samples in a circulating air oven and retesting specific physical properties to evaluate performance degradation under high-temperature and dry conditions. This aging test is conducted at 140 ± 2°C for 22 hours.
Wet Heat Aging Test - Test L
Wet heat aging testing places sponge samples in a circulating air chamber at 50 ± 2°C and 95 ± 5% RH for 22 hours to evaluate performance degradation under humid heat conditions.
Recovery Time - Test M
Test M is used to determine the recovery time of slow-recovery (viscoelastic) foam. The test uses an IFD device, where a circular platen is lowered onto the specimen surface and a preload force of 4.5 ± 0.5 N is applied. The specimen is compressed to 75% of its original thickness at a speed of 1000 mm ± 100 mm/min and held for 60 ± 3 seconds. The platen is then returned to the 5% position at the same speed. The time required for the specimen to recover to the preload force of 4.5 ± 0.5 N is defined as the recovery time.
Hysteresis Loss - Test N
Hysteresis loss testing can be performed using either IFD or CFD. Taking IFD as an example, a preload force of 4.5 ± 0.5 N is first applied to the top of the specimen, and the initial thickness is measured. The specimen is then compressed to 75% of its original thickness at a speed of 50 ± 5 mm/min and immediately released at the same speed until fully recovered. The difference between the areas under the loading and unloading curves represents the energy loss.
Hysteresis loss measures the reduction in the ability of flexible foam to recover its original support properties after compression.
Polyurethane foam performance testing involves various test items, and each standard has different test methods. SATISFY provides multiple foam performance testing services and can develop customized testing solutions according to customer requirements. Please contact SATISFY customer service for further information.
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