Every multi-material product design reaches the moment when the elastomer must be specified. At that moment, two parallel questions exist: which material is chemically compatible with the substrate, and which material delivers the functional properties the design requires. The best selection approach treats these as sequential filters — compatibility first, function second — rather than simultaneous trade-offs. A material that cannot bond to the substrate is not a candidate regardless of its Shore hardness or cost.

The Compatibility Filter: What Eliminates Candidates Immediately

The substrate material determines which elastomers remain in consideration. Before evaluating any functional properties, apply the compatibility filter:

Does the substrate have polar surface chemistry?

Polar substrates (ABS, PC, PA, PET, PBT, rigid PVC) are compatible with polar elastomers: TPU, SEBS (on ABS/ABS-PC), COPE (on PC/PET/PBT), PEBA (on PA). Multiple candidates remain after the first filter.

Non-polar substrates (PP, HDPE, LDPE) are not compatible with polar elastomers in standard overmolding. The filter eliminates TPU and most TPE sub-classes except polyolefin-compatible compounds. For PP: TPO. For HDPE/LDPE: adhesive bonding with CPO primer, or specialty polyolefin-matrix TPE.

Does the substrate have a specific chemistry match with one TPE sub-class?

Some substrates have a chemically direct match with a specific TPE sub-class:
– ABS ↔ SEBS (styrenic chemistry)
– PA ↔ PEBA (amide chemistry)
– PET/PBT ↔ COPE (ester chemistry)
– PP ↔ TPO (polyolefin chemistry)

When such a match exists, the matched TPE sub-class achieves cohesive failure through direct chemistry and is the natural first candidate. TPU also bonds to ABS, PA, and PET through its urethane mechanism — TPU is not eliminated, but the chemistry-matched TPE has a structural compatibility advantage.

After the Compatibility Filter: Applying Functional Requirements

Once the compatible elastomers are identified, functional requirements narrow the choice:

Mechanical durability. TPU excels here. Abrasion resistance, tensile strength, and tear resistance are higher for TPU than SEBS or COPE at equivalent Shore hardness. For applications where the elastomeric zone will experience sustained mechanical stress — tool handles under repetitive grip, footwear soles under cyclic loading, cable jacketing under flex fatigue — TPU’s mechanical properties are the differentiating factor.

Service temperature. This filter eliminates standard SEBS and TPU from high-temperature applications:
– Up to ~80°C: SEBS, standard TPU, PEBA, TPO are all viable
– Up to ~100°C: COPE in select grades; high-performance TPU grades
– Up to ~140°C: COPE specifically; other sub-classes not applicable
– Below -30°C: PEBA and low-temperature TPU maintain flexibility; standard SEBS and COPE may stiffen

Moisture and hydrolysis resistance. Ether-based TPU is the specification for sustained moisture exposure, sweat contact, or aqueous fluid contact. Ester-based TPU is not appropriate for these environments. SEBS has adequate moisture resistance for most non-immersion applications. COPE’s ester chemistry is susceptible to hydrolysis.

Chemical resistance (specific fluids). This filter depends entirely on the specific fluid. Consult supplier chemical resistance data with the actual fluid, concentration, and temperature. General guidance:
– Petroleum hydrocarbons: NBR-phase TPV or specialty TPU (not standard SEBS or COPE)
– Aqueous fluids, cleaning agents: Ether TPU, SEBS, EPDM-phase TPV
– Hydraulic fluids: PEBA, ether TPU (verify by fluid type)

UV and weather resistance. SEBS’s saturated midblock provides inherent UV stability without additives. TPU requires UV stabilizer packages for outdoor applications. COPE requires UV stabilizers. For outdoor applications: specify UV-stabilized grades of whichever elastomer the compatibility filter selected.

Regulatory compliance. Food contact (FDA 21 CFR), medical contact (ISO 10993), or toy safety (EN 71) requirements filter to specific compliant grades within the compatible elastomer set.

The TPU Advantage: When Breadth Matters

TPU’s advantage in the material selection process is breadth. It bonds reliably to ABS, PC, PA, PET, PBT, and rigid PVC — covering the most common engineering plastic substrates in a single material specification. For product development teams that work across substrate types, TPU provides consistent compatibility without sub-class switching.

When is TPU the selection:
– PA substrate with abrasion resistance requirement (TPU exceeds PEBA in abrasion performance)
– ABS substrate with thin-wall overmold where TPU’s higher tear strength prevents tearing during demolding
– Product portfolio with ABS, PC, and PA substrates requiring a single elastomer specification
– Applications requiring Shore hardness above 50D (beyond most TPE sub-class ranges)

The TPE Sub-Class Advantage: When Match Quality Matters

Chemically matched TPE sub-classes provide a direct bond at the molecular level that TPU’s urethane mechanism matches through indirect polar interaction. On substrates with a direct chemistry match:

• SEBS on ABS often produces higher measured peel strength than TPU on ABS at equivalent Shore hardness
• PEBA on PA provides more reliable bonds across a wider mold temperature range than TPU on PA
• TPO on PP is the only practical approach for cohesive failure bonds on polypropylene

When is the matched TPE sub-class the selection:
– Cost-sensitive ABS applications where SEBS’s lower cost per kilogram matters
– PA substrates in high-volume production where PEBA’s process latitude reduces rejects
– PP substrates where cohesive failure is required (TPO, not TPU)
– High-temperature applications on PET substrates where COPE’s temperature ceiling is required

When Process Constraints Drive Selection

In some production environments, process constraints override material preference:

Shared press capacity: If the only available press is configured for SEBS/ABS two-shot and the project requires PA substrate, the process needs PEBA or TPU — not SEBS.

Volume and tooling economics: Low-volume projects may not justify two-shot tooling; insert molding or adhesive bonding with a wider material selection may be economically necessary.

Certification timeline: If one material family already has regulatory documentation and the other does not, the certified material is selected on timeline grounds even if the other might offer a marginal performance advantage.

These constraints are legitimate selection inputs — the goal is a production-viable solution, not theoretical optimality.

For material selection support across your specific substrate portfolio and production constraints, Email Us.

Incure’s adhesive and coating formulations support the full range of TPU and TPE-substrate bonding combinations encountered in product manufacturing, including adhesion promoters that improve bond quality where direct chemistry matching is not available. For technical guidance, Contact Our Team.

Visit www.incurelab.com for more information.