Under ASTM D2000, both the BA and CA Type/Class designations resolve to ethylene propylene rubber, but the Type letter fixes the heat-aging test temperature and therefore the upper service-temperature envelope of the compound [S3]. The Class letter "A" on both BA and CA carries the same meaning: "no requirement" for volume swell after 70-hour immersion in IRM 903 oil, since EPDM is not an oil-resistant polymer family [S4][S5].
The Type/Class system within D2000 is constructed as a two-character cell: the first letter (Type) sets the heat-aging test temperature from 70°C (A) up to 300°C (K), and the second letter (Class) sets the maximum allowable oil swell from "no requirement" (A) down to 10% (K) [S4]. Because the polymer selection is implicit in the cell, BA and CA both steer the compounder toward EPDM, with the operating-temperature limit being the only meaningful difference.
Decoding the Line Callout Structure
A complete ASTM D2000 line callout reads ASTM D2000-3 M2BA714A14B14EO14EO34F17, parsed as: revision year (2003), metric units (M), grade 2, Type B, Class A, 70 Shore A durometer, 14 MPa minimum tensile strength, and a suffix string that adds heat-resistance, compression-set, fluid-resistance, and low-temperature tests [S2][S4]. When "M" is present, tensile strength is stated in MPa and temperatures in °C; without M, psi and °F apply, with 1 MPa = 145 psi for quick conversion [S2][S3].
Grade 1 compounds must only meet the basic D2000 requirements; grades 2 through 8 progressively add suffix tests such as ozone resistance, low-temperature brittleness, or fluid resistance, and a missing or non-1 grade number signals the most basic acceptance level [S3][S4]. The suffix letters carry their own table: A = heat resistance, B = compression set, C = ozone or weather, EO = oil fluid resistance, F = low temperature, and so on through Z for special requirements [S5].
BA vs CA on Heat Aging and Oil Resistance
BA and CA differ only in the Type column: B tests heat aging at 100°C and C tests at 125°C, both for 70 hours, with the same pass criteria of ±30% tensile-strength change, ±50% maximum hardness change, and ±15 durometer points hardness change [S4][S5]. Class A in both cells means "no oil-swell requirement," consistent with EPDM's known weakness in petroleum oils and strong performance in water, steam, and polar fluids [S3].
For EPDM used in EPDM rubber sealing applications, this is the practical rule: if your service temperature is at or below 100°C, BA is the correct and least-expensive callout; if your continuous exposure sits between 100°C and 125°C, switch to CA so the post-aging tensile and hardness values stay within spec [S3][S4]. Either callout is appropriate for steam, hot water, phosphate-ester hydraulic fluids, brake fluids, and dilute acids or alkalis, where EPDM outperforms NBR and neoprene [S1].
Hardness, Tensile, and Suffix Selection
After the Type/Class cell, the next two digits fix hardness and tensile strength: 70 means 70 ±5 Shore A, 14 means 14 MPa minimum tensile, and these are the typical values engineers see on EPDM 70-durometer O-rings and gaskets [S2]. A Shore A 70 EPDM is the workhorse grade; for softer seals specify 60 (60A), and for high-pressure extrusion resistance specify 80 or 90 [S1][S2].
For sealing duty, append the suffixes that match the service environment: A14 tightens heat-resistance delta after 70 hours at the Type test temperature, B14 sets compression-set testing (critical for O-rings under sustained squeeze), EO14 / EO34 covers IRM 901 and IRM 903 oil immersion where some hydrocarbon exposure is unavoidable, and F17 adds low-temperature brittleness testing for cold-start applications [S2][S4]. Skipping B14 on a static seal is a common cost-cut that backfires once the gland geometry holds the rubber under constant deflection; compression set is the failure mode, not tensile [S3].
Where BA and CA Fit (and Where They Don't)
BA-grade EPDM is the default for plumbing seals, HVAC gaskets, water-pump O-rings, food-grade dairy fittings, and roofing membranes where the continuous temperature stays at or below 100°C and no petroleum-oil contact exists [S1][S3]. CA-grade EPDM is the right call for under-hood automotive coolant hoses, steam-service gaskets, and certain heat-pump or solar-thermal seals where the upper end of the 100-125°C band is reached during normal operation [S3][S4].
Do not specify BA or CA EPDM for any service that exposes the elastomer to gasoline, diesel, mineral oil, or synthetic compressor oil; the A Class allows unlimited swell, and the EPDM will soften and extrude within days under such exposure, and a BC, BE, BF, or BG callout (chloroprene or NBR) is the correct alternative [S3][S5]. Likewise, if the application needs 150°C continuous exposure, step up to Type D (DA = ethylene propylene at 150°C test) or leave the EPDM family entirely for a fluorocarbon or silicone [S4].
Comparison Table: BA vs CA EPDM at a Glance
The following matrix lines up the two callouts against the four criteria that drive most EPDM seal selections: [S4]
1. Heat-aging test temperature: BA = 100°C, CA = 125°C. 2. Oil-swell requirement (IRM 903, 70 h): BA = none, CA = none. 3. Typical polymer: BA = EPDM, CA = EPDM. 4. Continuous service temperature ceiling: BA = ~100°C, CA = ~125°C. 5. Steam / hot-water / brake-fluid compatibility: BA = suitable, CA = suitable. 6. Petroleum-oil compatibility: BA = not suitable, CA = not suitable [S3][S4][S5].
Decision rule from the matrix: pick BA when maximum continuous temperature stays at or below 100°C and you want the lowest-tendered compound; pick CA when the operating temperature regularly enters the 100-125°C band and you need the 125°C heat-aging data on the certificate of analysis to satisfy your QA review [S3][S4].
Cross-Reference Within the D2000 Family
The D2000 table also contains DA (ethylene propylene at 150°C test), AK (EPDM, high-temp SBR, butyl at 100°C), and AA (natural rubber / SBR / butyl at 70°C), so the EPDM family is not limited to BA and CA; DA is the next step up if you need higher-temperature headroom and can tolerate the cost premium [S3][S5]. For peroxide-cured EPDM used in drinking-water service, NSF/ANSI 61 and WRAS certifications overlay the D2000 callout and may force a specific compound recipe independent of the cell letter [S1].
Engineers familiar with hydraulic port sealing know that the wrong elastomer choice shows up first as extrusion or swell, and the same principle governs EPDM selection: match the Type/Class cell to the thermal and chemical envelope, then add suffixes for the specific test data your QA team will audit on each lot.
Sourcing and Standards Discipline
When issuing a purchase order, list the full callout including suffix requirements rather than just "EPDM 70 durometer," because the cell letter alone (BA or CA) does not encode hardness, tensile, compression set, or fluid resistance, all of which must be carried as separate digits and suffix letters [S2][S4]. Require the supplier to provide a certificate of analysis referencing the ASTM D2000 edition year (for example, ASTM D2000-3) and the specific test results for each suffix [S1].
Two spec-engineering signals worth tracking on parts dated within the past six months: more automotive coolant and heat-pump OEMs are migrating from BA to CA callouts as under-hood temperatures climb with electrified powertrains, and water-utility RFPs are increasingly appending WRAS or NSF/ANSI 61 suffix-style requirements to BA-class EPDM gaskets [S1][S4]. The next verification node for any EPDM qualification remains the original ASTM D2000 text and the supplier's per-lot CoA against the stated suffix table.
Spec-level background on the components involved: pressure transmitter, and flow meter.