Skin permitted on top/bottom. Compress 50±1% for 46 h ±30 min. Remeasure 24 h ±15 min after removal.
Flame §15
7±1 × 12.7±1 × 125±5 mm
7 ± 1 mm
Horizontal. Blue flame 38±2 mm. Apply 60±1 s; record propagation time. Avg of 3 specimens.
Shrinkage §16
~300 × 75 mm; 3 specimens
As received
Benchmarks ~250 mm apart. 7 days at 70±2°C. Condition ≥24 h before, ≥2 h after oven.
Oil Aging §18
Round Ø 41.3 ± 1 mm
6.4 – 28.6 mm
IRM 902 oil (D471). 70 h ±30 min at 70±2°C. Blot lightly immediately after; measure volume.
Flexing — Suffix H
~50 × 50 × 25 mm
~25 mm
250,000 cycles at 50% amplitude. Triplicate; average. Calc. comp. set per D1055 §19.
Standard test conditions (§10): 23 ± 2°C (73.4 ± 3.6°F), 50 ± 10% RH. Condition specimens ≥ 22 h prior to testing.
Warning (§19.1): Data from interlaboratory study of D6576-07, conducted 2012. Nine labs, three materials, duplicate results per lab, per Practice E691. These data shall not be rigorously applied to lot acceptance/rejection. Generate lab-specific data per E691. Research Report: ASTM RR:D20-1261.
Table 5 — Recovery: 50% Compression, 46 h @ RT, 24 h Recovery (%)
Material
Average x̄
Repeatability s_r
Reproducibility s_R
Repeatability Limit r
Reproducibility Limit R
Material A
74.503 %
0.907
1.578
2.540
4.420
Material B
91.467 %
0.868
1.025
2.430
2.870
Material C
86.449 %
0.512
1.612
1.435
4.513
Table 6 — Oil Aging (IRM 902, 70 h @ 70°C): % Change in Volume
Material
Average x̄
Repeatability s_r
Reproducibility s_R
Repeatability Limit r
Reproducibility Limit R
Material A
8.540 %
0.994
5.174
2.782
14.487
Material B
6.798 %
0.555
3.440
1.555
9.631
Material C
9.882 %
0.504
4.060
1.410
11.369
Table 7 — Shrinkage (7 days @ 70°C): % Change in Length & Width
Material
Average x̄
Repeatability s_r
Reproducibility s_R
Repeatability Limit r
Reproducibility Limit R
Material A
2.436 %
0.293
0.490
0.820
1.372
Material B
3.221 %
0.251
0.587
0.703
1.644
Material C
4.218 %
0.224
0.525
0.628
1.470
Interpretation Guide
Term
Definition
x̄
Average of all laboratories' calculated averages for that material
s_r
Repeatability std dev — within-lab variability under constant conditions
s_R
Reproducibility std dev — between-lab variability
r
= 2.8 × s_r. Max acceptable difference between two results from the same lab (95% confidence)
R
= 2.8 × s_R. Max acceptable difference between two results from different labs (95% confidence)
Table X2.1 — Visual Inspection
MIL STD 105 Level I. Sample unit = one sheet or molded part. AQL: 2.5 major / 6.5 total defects per 100 units.
Category
Defect
Major
Minor
Appearance
Not uniform in texture, finish, or firmness
✕
Dirt, foreign material, embedded particles
✕
Production defects not corrected (§6.1)
✕
Construction
Defects per MIL STD 293
✕
✕
Skin or rind not as specified
✕
Odor
Objectionable odor
✕
Table X2.2 — Dimensional Inspection
MIL STD 105 Level S-3. AQL: 1.5% defective.
Examination
Defect
Sheets and molded parts
Any dimension varying more than ± tolerances specified in §8 / Table 3
Table X2.3 — Physical Properties Inspection
Failure to pass any requirement = cause to reject the entire lot. All results reported as averages.
Property
Req. Ref.
Test Section
Specimens
Report To:
Basic (Mandatory) Test Methods
Compression Deflection
Table 1
§11 / D1056 §17-22
3
0.1 kPa (psi)
Low-Temperature Resistance
Table 1
§12 / D1056 §57-61
3
Pass/Fail
Accelerated Aging
Table 1
§13 / D1056 §35-41
3
1%
Recovery
Table 1
§14
3
1%
Flame Resistance
Table 1
§15 / D635
3
1 s
Shrinkage
Table 1
§16
3
1%
Water Absorption (Type 2 only)
Table 1
§17 / D1056 §43-48
3
1%
Oil Aging
Table 1
§18 / D471
2
1%
Odor
Table 1
§20 / SAE J-1351
1
Use rating chart
Non-Mandatory (Suffix-Triggered)
Flexing — Suffix H
Table 2
X1.3 / D1055 §24-26
3
%
Free Sulfur — Suffix Y
Table 2
X1.2 / D297
3
%
Apparent Density — Suffix W
Table 2
X1.1 / D1056
3
0.001 kg/m³
Table X2.4 — Packaging Inspection
MIL STD 105 Level I. AQL: 4.0% defective. Max box weight: 90.7 kg (200 lb).
Examine
Defect
Packaging — Sheets
Paper separator sheets omitted
Packaging — Molded Shapes
Not wrapped, boxed, or protected against abrasion/deformation; package or material not as specified
Packing
Not per contract; wrong quantity/arrangement; nonconforming/missing components; incomplete closures; loose or inadequate strapping; bulged or distorted containers
Count
Less than specified or indicated quantity
Weight
Gross weight exceeds requirements
Markings
Interior/exterior markings omitted, illegible, incorrect, incomplete, or not per contract; precautionary markings missing
Sheet material: one side only, rows ≤ 12.7 cm (5 in.) apart, characters ≥ 9.53 mm (0.375 in.) high.
Age control: Do NOT deliver to government when more than 4 quarters old from cure date (§X2.2).
What Is ASTM D6576?
ASTM D6576 is the Standard Classification System for Chemically Blown Cellular Rubber. It provides designation codes for sponge rubber materials produced by chemical blowing agents rather than by mechanical expansion. The standard classifies these materials by compound type, density, hardness, and compression set, enabling engineers and purchasers to specify blown cellular rubber without reference to a proprietary product name.
Chemically blown cellular rubber is commonly used in automotive sealing, HVAC duct sealing, refrigeration gaskets, and industrial gasketing where a compressible, conformable seal is needed. The standard does not restrict or encode the base elastomer in the designation — any synthetic rubber compound meeting the physical requirements may be used, except that Grade A material shall not contain natural rubber (§6.2.2).
ASTM D6576 vs ASTM D1056
D6576 and D1056 are both cellular rubber standards, but they cover different manufacturing processes. D1056 covers sponge and expanded rubber produced by any process (mechanical, physical, or chemical expansion), while D6576 specifically addresses chemically blown cellular rubber where a chemical blowing agent is incorporated into the compound and activates during cure. D6576 designations are not directly interchangeable with D1056 designations.
A = oil- and flame-resistant; B = no oil, flame, or low-temp requirement; C = low-temperature resistant (−55°C), oil and flame not required
Condition
Super Soft, Soft, Soft-Medium, Medium, Medium-Firm, or Firm
Compression-deflection range (stiffness) at 25% deflection per Table 1
Suffix letters (optional)
H, O, W, Y
Optional requirements: H = flexing/compression set; O = odor; W = density; Y = sulfur content ≤0.60%
The D6576 designation does not encode the base elastomer type. Any qualifying synthetic rubber compound may be used. The designation fully describes cell structure, service grade, and firmness — the compounder selects the polymer to meet those performance requirements.
Common Applications for ASTM D6576 Blown Cellular Rubber
Automotive door and window seals: EPDM blown sponge provides a soft, conformable seal against irregular body panel gaps.
HVAC duct gaskets: Low-density blown cellular rubber seals duct flanges against air leakage.
Refrigeration door gaskets: Closed-cell chemically blown rubber resists moisture ingress in cold storage seals.
What is the difference between chemically blown and mechanically expanded cellular rubber?
Chemically blown cellular rubber (classified by D6576) is made by incorporating a chemical blowing agent into the rubber compound that releases gas during vulcanization, creating the cell structure as the rubber cures. Mechanically expanded rubber uses physical processes or pre-formed gas pockets. The resulting materials differ in cell uniformity, density control, and surface skin characteristics.
Is ASTM D6576 the same as ASTM D1056?
No. D6576 specifically covers chemically blown cellular rubber, while D1056 covers a broader range of sponge and expanded rubber materials regardless of manufacturing process. Designations from these two standards are not interchangeable. When a drawing calls out a D6576 designation, the material must meet D6576 requirements specifically.
What rubber compounds are covered by ASTM D6576?
ASTM D6576 does not specify or restrict which elastomer must be used, nor does it encode the polymer type in the designation. Any synthetic rubber compound capable of meeting the physical requirements of the applicable Type, Grade, and Condition may be used. The one explicit restriction in the standard is that Grade A material shall not contain natural rubber (§6.2.2). The compounder selects the base elastomer based on the service requirements.
How is compression set used in a D6576 designation?
D6576 does not use a compression set digit in its designation. Instead, the standard specifies a Recovery requirement in Table 1: Type 1 (open cell) must recover to at least 90% of original thickness, and Type 2 (closed cell) must recover to at least 60%, both measured 24 hours after 46 hours of 50% compression at room temperature. Optional Suffix H adds a flexing/compression set requirement per D1055. The designation itself encodes only Type, Grade, and Condition — not a compression set class number.
Reference tool provided by Hanna Rubber Company, Kansas City, MO — distributor of rubber, gasket, hose, and sealing products since 1925. For cellular rubber material sourcing or custom sponge gasket fabrication, contact Hanna Rubber. Always verify final specifications against the current published ASTM D6576 standard.