Compounded EPDM rubber density spans 0.90 to over 2.00 g/cm³, equivalent to 900 to 2000+ kg/m³, with the spread driven by carbon black, mineral fillers, plasticiser oil, and polymer-specific gravity, per the standard property table on EPDM rubber [S4]. A 70 Shore A commercial sheet sold for gasketing typically lands at 1.22 to 1.50 g/cm³ [S1][S5], while roofing-membrane EPDM samples cut from a 6 mm roll measure roughly 1.20 g/cm³ at bench scale [S3].
Cellular and sponge variants invert the picture: soft expanded EPDM/NR sponge runs 115 kg/m³, with denser closed-cell grades still under 200 kg/m³, far below the solid compound [S2]. Anyone buying EPDM by weight, by roll, or by kg-of-stock per gasket should pin the form (solid vs sponge) and the hardness before trusting a number from a generic density table.
What the EPDM density range actually means
The polymer backbone of EPDM is ethylene-propylene-diene with 2-12% diene content (ENB, DCPD, or VNB) per the polymer overview on EPDM rubber [S4]. That base gum has a specific gravity close to 0.86 g/cm³, so a 1.50 g/cm³ sheet is not 0.64 g/cm³ of EPDM, it is roughly 0.86 g/cm³ of EPDM gum plus 0.64 g/cm³ of filler and oil, the rest being the heavier carbon black and mineral load that gives EPDM its mechanical strength.
Suppliers quote three different numbers on the same product line: 1.13 g/cm³ for a generic EPDM average [S7], 1.4 to 1.5 g/cm³ for a filled rubber-grade table [S1], and 1.22 to 1.30 g/cm³ for a specific 70 Shore A sheet (density 1.22 g/cm³, specific gravity 1.30 g/cm³ listed side-by-side on the same datasheet) [S5]. The 1.13 g/cm³ figure is the lowest of the three and is consistent with a lightly filled, peroxide-cured extrusion compound. The 1.4-1.5 g/cm³ range is the carbon-black-loaded, sulfur-cured sheeting compound that dominates roofing and gasketing.
The 0.90 to over 2.00 g/cm³ envelope stated in the standard property table covers the full design space: a 0.90 g/cm³ compound is achievable with high oil extension and light filler load, while values above 2.00 g/cm³ come from heavy baryte, silica, or specialty filler systems used for acoustic-damping or radiation-shielding grades [S4].
Solid EPDM vs EPDM sponge: density comparison
The table below lines the main EPDM product forms up against the three decision criteria that drive weight-out calculations: typical density in kg/m³, the unit weight on a standard 6 mm × 1 m² sheet, and the dominant application. [S3]
Solid EPDM, general purpose (70 Shore A): 1220 to 1500 kg/m³; 6 mm sheet ≈ 7.3 to 9.0 kg/m²; gaskets, roofing, weatherstrip. Solid EPDM, high-filler acoustic: 1500 to 2000+ kg/m³; 6 mm sheet ≈ 9.0 to 12.0+ kg/m²; acoustic damping, ballast. EPDM roofing membrane (compounded, 6 mm sample): roughly 1200 kg/m³ [S3]; 6 mm sheet ≈ 7.2 kg/m²; single-ply roofing. Soft expanded EPDM/NR sponge, flame-resistant: 115 kg/m³ [S2]; 6 mm sheet ≈ 0.69 kg/m²; HVAC seals, expansion joints. Denser closed-cell EPDM sponge: 150 to 200 kg/m³; 6 mm sheet ≈ 0.9 to 1.2 kg/m²; gasket backer, cushioning.
Two practical takeaways from that table. First, switching a 6 mm solid gasket (about 8 kg/m²) to a 6 mm soft sponge (about 0.7 kg/m²) cuts the mass-per-area by a factor of roughly 11, a real freight and handling number, not a marketing one. Second, if the datasheet only says "EPDM" without a form qualifier, ask which form. A sponge at 115 kg/m³ and a solid at 1500 kg/m³ share a polymer name and a 13× density gap, and that gap is the single most common source of mismatched specifications on incoming-material inspections.
Hardness, filler loading, and how density tracks with Shore A
EPDM hardness spans 30 to 90 Shore A in commercial compounds [S4], and density moves with it because higher hardness is almost always bought through higher filler load, not higher base-polymer crosslink density. A 40 Shore A weatherstrip profile can sit at 0.95 to 1.05 g/cm³ with light calcium carbonate and high paraffinic oil extension; a 70 Shore A sheeting grade sits at 1.22 to 1.30 g/cm³ [S5]; an 80 Shore A dense gasket compound pushes past 1.40 g/cm³ with heavy carbon black.
Two caveats engineers should keep in mind. The first is that specific gravity and density are not the same number, even though they look interchangeable. One supplier lists 1.22 g/cm³ as density and 1.30 as specific gravity on the same 70 Shore A sheet [S5]; that 0.08 gap is the difference between the apparent mass per unit volume (density, includes any closed porosity) and the ratio of the compound's mass to the mass of an equal volume of water (specific gravity, dimensionless). For gasket compression-set and sealing calculations, use the density figure, not the specific gravity.
The second caveat is plasticiser migration. EPDM is routinely extended with 20-50 phr (parts per hundred rubber) of paraffinic oil, and density in service can drift slightly as the oil migrates toward the surface over years of thermal cycling. For long-life sealing (rail, aerospace, underground cable joints), the as-compounded density is the number to specify, not the as-tested density of a fresh sample.
Where each EPDM density grade is used in practice
Roofing-membrane EPDM at roughly 1.20 g/cm³ (1200 kg/m³) is the workhorse of single-ply roofing in North America and Europe [S3]. The 6 mm sample tested in the FSRI database gave specific heat 1379-1459 J/(kg·K) at 10-40 °C and thermal conductivity 0.133-0.144 W/(m·K) at 15-45 °C, useful numbers for any heat-flow calculation across a roof assembly [S3]. A 6 mm membrane sheet therefore weighs about 7.2 kg/m², which sets the ballast load for mechanically attached or fully adhered systems.
Automotive weatherstrip and door seals run lighter. A 60-65 Shore A extrusion compound typically sits at 1.05 to 1.15 g/cm³, with EPDM/NR sponge weatherstrip at 115-200 kg/m³ for the soft bulb behind the dense skin [S2]. The combination of a dense outer skin (about 1100 kg/m³) bonded to a soft cellular bulb (about 150 kg/m³) is the reason a 5 mm weatherstrip profile can weigh 0.4-0.6 kg/m rather than the 5-6 kg/m a solid profile of the same thickness would weigh.
For EPDM sponge grades specifically, the 115 kg/m³ soft expanded product is rated for moderate-temperature, CFC- and HCFC-free applications with flame resistance [S2]. Denser closed-cell EPDM sponge at 150-200 kg/m³ is commonly cut into gasket backer strips, where compressibility (not mass) is the design driver, but the density still matters because compressive strength at 25% deflection scales roughly with density for closed-cell foam.
Standards, sourcing notes, and the data behind the numbers
EPDM is classified as an M-Class rubber under ASTM D-1418, which covers elastomers with a saturated polymethylene backbone [S4]. That classification is what makes EPDM chemically compatible with hot water, steam, phosphate ester hydraulic fluids, and dilute acids, and incompatible with petroleum oils, fuels, and bituminous material, the last being a well-known field failure mode for EPDM gaskets on asphalt-shingle roofs [S4].
The 0.90 to over 2.00 g/cm³ density envelope in the standard property table is not a single test result but a design range compiled from published compound data sheets [S4]. The 1.4-1.5 g/cm³ figure in rubber-grade tables [S1] is the filled-compound average, the 1.13 g/cm³ figure [S7] is a typical-compound average skewed toward extrusion-grade gum, and the 1.22-1.30 g/cm³ pair [S5] is one specific 70 Shore A product. Engineers specifying EPDM for a new gasket should request a batch certificate with the actual measured density, not a generic range, because the 0.86-1.50 g/cm³ span across these sources is wider than the tolerance stack-up on most compression-set calculations.
For anyone buying EPDM by weight-to-volume conversion, a single 1.0 g/cm³ assumption is risky. A 6 mm solid EPDM gasket cut from 1.22 g/cm³ stock weighs 7.3 kg/m², while the same gasket cut from 1.50 g/cm³ stock weighs 9.0 kg/m², a 23% mass penalty that shows up directly in freight, in container loading, and in the inertia calculation for moving seals. Pair the density on the certificate with the Shore A and the compound family (sulfur vs peroxide cure) before releasing the PO.
Failure modes and limits to watch when density drifts out of spec
Density outside the supplier's stated range is a fast, cheap incoming-inspection proxy for filler or polymer substitution. A batch of 70 Shore A EPDM that comes in at 1.05 g/cm³ when the datasheet says 1.22 g/cm³ [S5] has either lost filler, gained plasticiser oil, or been blended with a lower-specific-gravity polymer such as EPM, which sits at 0.9 g/cm³ in unfilled form [S1]. All three changes degrade tensile, compression set, and aging performance, even if the Shore A number still passes.
Conversely, a batch that comes in at 1.60 g/cm³ against a 1.30 g/cm³ datasheet has been over-filled, which raises hardness, raises modulus, and usually kills elongation at break. The ≥300% elongation minimum typical of EPDM vulcanisates [S4] is the next test to run once density is suspect, and it will fail in the same direction as the density overshoot.
For the foam side, a sponge sample that comes in at 250 kg/m³ against a 115 kg/m³ datasheet [S2] has either been compressed in storage (recovery test needed) or was never the grade ordered. Closed-cell EPDM sponge recovers most of its original thickness within 24 hours at room temperature; a sample that stays at 250 kg/m³ after 24 hours of free recovery is a different product, and the seal compression profile will not match the drawing.
Next signals to track: ASTM D1418 revision activity around the M-class EPDM designation, and any new FSRI or vendor batch data that brackets the 1.20-1.50 g/cm³ range for filled 60-70 Shore A compounds, since that is the band where most industrial gasket and roofing specifications land. For broader elastomer comparison context, the industrial rubber and silicone rubber encyclopedia entries cover how EPDM density stacks against NBR, FKM, and silicone across the same Shore A range.
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