Extruded rubber profile selection is driven by four spec gates — polymer family, cross-section form, tolerance/dimension, and operating environment (temperature, fluid, UV, flame) — and the cheapest profile that passes all four almost always wins on $/metre [S1].
OEMs commonly quote five profile geometries: sponge/foam extrusion, solid/compact extrusion, co-extruded seal strip, PVC & rubber compound extrusion, and metal-inserted profiles, with minimum order quantities starting around 1000 m on China-sourced lines and supply capability up to 10,000 m/day on high-volume programmes [S1]. The polymers offered by multi-material extruders cover silicone, CR (neoprene), NBR, and EPDM as the working shortlist [S1], while single-polymer specialists (for example silicone-only houses) trade breadth for tighter cure control and lot-to-lot consistency [S2].
Match Polymer Family to Fluid and Temperature Duty
Polymer choice is the first decision gate and is set by the chemical and thermal envelope, not by price: EPDM is the default for outdoor weathering, hot water, steam, and phosphate-ester hydraulic fluids; NBR is the default for petroleum oils, diesel, and grease where temperatures stay below roughly 100 °C; CR (neoprene) covers moderate oil resistance plus good flame and ozone performance; silicone is selected for sustained high temperature, food/medical contact, and low compression set across a wide thermal range [S1][S2]. Specifying a single elastomer that meets both an oil-exposed flange and a UV-exposed door seal is the classic over-spec that inflates unit cost; the more common solution is a co-extrusion or dual-durometer strip that puts each polymer where the duty is [S1].
Cross-check the polymer against published temperature limits: silicone grades routinely cover -60 °C to +200 °C continuous, EPDM typically -50 °C to +130 °C with hot-water/steam peaks above that, NBR generally -30 °C to +100 °C, and CR roughly -35 °C to +110 °C; the values are generic ranges, so a project-specific TDS is still required [S1][S2]. For a primer on how these families differ at the molecular level, see the nitrile rubber and silicone rubber reference entries.
Pick the Cross-Section Form: Sponge, Solid, Co-extruded, Metal-inserted
Profile geometry is the second spec gate: sponge/foam extrusions are used where compression recovery and acoustic/thermal insulation matter more than a fluid barrier; solid/compact extrusions carry mechanical load and form the pressure side of a seal; co-extruded strips combine a soft sealing bulb with a rigid carrier in one continuous pass; metal-inserted profiles add a steel or wire core for retained shape, captive fitment, or magnetic sealing [S1]. The same extruder can typically run all four with a die swap, so form selection is a tooling question more than a sourcing question.
Durometer and density targets belong on the same drawing as the section drawing: a 30–50 Shore A sponge bulb paired with a 60–80 Shore A carrier is a common co-extrusion pairing for door and enclosure seals, while solid profiles for hydraulic or pneumatic service usually sit at 70±5 Shore A with specific compression-set and tensile/elongation limits called out per the project TDS. Tolerances on free height are typically ±0.25 mm on small sections and ±0.5 mm on larger sections for general industrial profiles; tighter tolerances require harder compounds and slower line speeds, which raise price per metre [S1].
Decision Matrix: Polymer vs Form vs Duty
A short criteria-based comparison helps buyers pick the right combination in one pass: (1) EPDM solid or co-extruded with EPDM sponge is the go-to for outdoor enclosure, HVAC, and automotive weather-seal use, with good UV/ozone resistance but poor resistance to petroleum oil; (2) NBR solid is the standard for oil-side lip seals, valve stem seals, and machinery boots where oil exposure is continuous and temperatures stay moderate; (3) silicone solid or sponge dominates food-grade, medical, and high-temperature gaskets, with the highest upper temperature limit but lower tear strength and higher cost per kilogram; (4) CR solid is a balanced choice where moderate oil, flame, and weather resistance are all required, including some rail and marine applications [S1][S2]. For a deeper background on the broader industrial rubber family, the reference page is the natural next read.
If the application involves prolonged sunlight, salt spray, or steam, EPDM or silicone beats NBR on every other axis; if the application is submerged in petroleum oil or diesel, NBR or CR is non-negotiable regardless of cost. A common rule of thumb on price per metre, for indicative sourcing only, is silicone ≥ CR ≈ EPDM > NBR, but actual quotes depend on durometer, section weight, and order volume rather than polymer alone [S1].
Who Should NOT Pick the Mainstream EPDM Default
EPDM is the right answer for roughly half of all extrusion RFQs, but it fails badly in three scenarios buyers often overlook: continuous contact with petroleum oil or gasoline (the polymer swells and loses mechanical strength), long-term exposure to concentrated acids or hydrocarbon solvents, and dynamic high-temperature steam above its upper continuous limit where peroxide-cured EPDM grades must be specified rather than sulphur-cured [S1]. A buyer who copies an EPDM part number into an oil-rich gearbox or a chemical-skid gasket and then runs it at 150 °C will see premature hardening, extrusion, and seal failure well before the expected service interval.
Equally, the default pick of "soft sponge everywhere" fails where the seal must carry a pressure differential, hold a captive clip, or resist pinch-off under repeated door or hatch cycling; in those cases a solid or metal-inserted carrier with a defined compression load is the correct geometry, and a soft bulb is added as a secondary sealing lip only if a fluid or acoustic barrier is also required [S1].
Standards, Tolerances, and Supplier Audit Points
Standards discipline matters more than price on safety-relevant seals: potable-water and food-contact profiles should be specified to the relevant FDA or WRAS family as the application requires, and automotive Tier-1 buyers will normally require IATF 16949 plus a PPAP-level control plan for any rubber extrusion that lands on a vehicle, while general industrial profiles can run under ISO 9001 only [S3]. Dimensional tolerance, hardness, tensile strength, elongation at break, compression set, and specific gravity should all be carried as numeric callouts on the drawing rather than left as "to supplier standard".
Audit the extruder on cure method (peroxide vs sulphur), post-cure cycle, batch traceability, and storage life before signing the PO: a peroxide-cured silicone sponge that has not been post-cured will continue to evolve acetic acid or peroxide residues and can corrode adjacent metal inserts, while a sulphur-cured EPDM stored past its shelf life will have lost a meaningful slice of its elongation at break before the profile is even installed. For EPDM-specific guidance on weathering and UV performance, the EPDM rubber reference is the right companion read. Adjacent equipment decisions (for example picking the right drive or pumping hardware in a seal-driven skid) can be cross-checked against spec-first selection maps such as this Overhead Bridge Crane vs Truck Crane: 2026 Spec Map when the seal is part of a larger mechanical assembly.
Lead Time, MOQ, and Sourcing Signals
Volume signals to verify up front: China-sourced multi-polymer extruders typically quote 1000 m MOQ with 10,000 m/day supply capability, payment by TT or LC, and FOB China main port [S1]; specialist silicone-only houses tend to quote smaller MOQs and shorter cure-development cycles, at a higher per-metre rate, and often run on a make-to-order rather than make-to-stock model [S2]. Both models are legitimate; the choice is governed by whether the project needs a 2-week sample-to-production loop or a 6-week tooling-plus-PPAP loop.
Trackable next signals: confirm the polymer TDS and cure system in writing before tool cut, lock hardness and compression-set limits on the print, request first-article dimensional reports against the agreed ISO 3302 (or equivalent) tolerance class, and require batch traceability through to raw-material lot. With those four documents on file, the part number is reproducible across extruders and the buyer is no longer captive to a single shop's cure window.