TPV vs. EPDM rubber

This is the comparison buyers ask about most, because EPDM is the default seal rubber and TPV is the usual thermoplastic replacement. For the wider field, see TPV vs. other elastomers.

TPV vs. EPDM side by side

Typical ranges; EPDM properties depend heavily on the compound (cure system, black and oil levels), and TPV properties on hardness and grade. Compare compression set only at the same test temperature, time and deflection.

Processing: cure vs. melt and freeze

EPDM is bought as a compound, mixed with filler, oil and a cure system, then shaped and cured. Molded parts go into a hot mold by compression, transfer or rubber injection and stay there until they cure; cure temperatures are typically around 160–200°C / 320–392°F. Extruded profiles run through a continuous cure line. Parts often need deflashing.

TPV arrives as ready-to-run pellets. It is dried at about 80°C / 176°F for 3 hours (4 hours with regrind) to 0.08% or less, melted at about 175–230°C / 347–446°F, and injected into a cool mold at about 10–66°C / 50–151°F, where it freezes rather than cures. Purge if the press idles longer than about 20 minutes. Full settings are in processing parameters by resin and the drying guide.

Shrinkage is the trap when converting a part. TPV flow-direction shrinkage falls from about 4.1% at 49A to 1.5% at 94A while cross-flow stays near 0.7%, so soft TPV parts shrink very differently along and across the flow. An EPDM tool cannot be reused; the new tool needs gating and cavity sizing designed for TPV.

Cycle time, scrap and cost per part

• Cycle time. A thick EPDM part may sit in the mold for minutes to cure. A TPV part of the same size is usually out much sooner, with the cycle set mainly by cooling time. Check with your own wall thickness.
• Scrap. TPV runners, startup parts and rejects can be ground and reused. Cured EPDM scrap and flash are waste or low-value filler.
• Secondary work. TPV usually needs no deflashing or post-cure, and color is added with masterbatch rather than by mixing a separate compound.
• Weight. At 0.97 vs. 1.25 g/cm³, the TPV part is about 22% lighter (0.97 ÷ 1.25 = 0.78). Use your own grades’ densities.
• Material price. TPV can cost more per pound than a commodity EPDM compound, so compare the cost per finished part, not per pound.

Compression set and high-temperature sealing

Compression set is the share of a squeeze a seal fails to recover after being held compressed at temperature. Lower is better. At room temperature and up to moderate heat, good TPV sealing grades come close to EPDM. As temperature rises, TPV’s compression set climbs faster, because the PP matrix creeps under load as it approaches its softening range. Test length matters too: some TPV grades compare better with EPDM in long tests than in short ones, so compare like with like. EPDM, crosslinked throughout, holds its recovery better when hot, and peroxide-cured EPDM is usually the best of the EPDM types for heat.

So ask for compression set at your service temperature and time, for example per ASTM D395 Method B, and compare both materials on the same conditions. A value measured at 23°C / 73°F says little about a seal that lives at 100°C / 212°F. If a seal is already taking a set, see seals losing compression.

When to choose TPV, and when to stay with EPDM

When to choose TPV

• Seals, boots, grommets and plugs that run below about 125°C / 257°F
• High volumes where cycle time and scrap reuse pay for a new tool
• Two-shot or co-extruded parts with a PP carrier, which TPV bonds to
• Weight-sensitive automotive parts
• Colored parts, or parts where flash and deflashing are a problem

When to stay with EPDM

• Long-term sealing above about 125°C / 257°F, or tight compression set limits when hot
• Steam, hot water under pressure, or glycol-based brake fluid
• Very soft seals below about 35A, or large sponge profiles
• Low volumes where existing rubber tooling is already paid for
• Parts approved by a customer in EPDM, where requalification costs more than the savings

Automotive and appliance examples

Automotive weatherseals. Vehicle programs commonly use both. Glass-run channels, belt-line seals, cowl seals and molded end caps are frequent TPV applications, often co-extruded or molded onto a PP or rigid carrier. Primary door and trunk seals, sponge bulbs and seals near hot zones are more often EPDM. Rack-and-pinion and other boots and air-duct bellows also use TPV. Automotive approvals are grade-specific, so ask for the grade’s documentation against your customer’s spec.

Appliances. TPV is used for grommets, feet, pump and sump seals, hose cuffs and molded gaskets in washers and dishwashers. Where a seal sits in hot water and detergent at high temperature for its whole life, such as some door boots and heater-zone seals, EPDM often remains the choice. Water and food-contact uses depend on the grade: ask for the producer’s FDA letter, or an NSF/ANSI 61 listing for potable water.

What to send us

• The EPDM compound or drawing callout the part uses now, and its hardness
• Service temperature, the fluids the part touches and the compression set it must meet
• Whether it is molded or extruded, and any carrier or substrate
• Automotive, food or water requirements
• Quantity and ship-to city

A polymer chemist reviews every request and checks the grade against your part, process and documents before we quote. Every lot ships with a COA, and orders start at one gaylord. Samples of about 50 lb are available upon credit approval. We aim to send your quote within one to three business days.

Common questions