Material selection for multi-material overmolding and bonding applications requires a systematic view of which elastomer-substrate combinations produce reliable adhesion, which require process intervention, and which should be avoided. The compatibility ratings below reflect the practical adhesion outcomes achievable in production injection molding and adhesive bonding applications — not laboratory-optimized conditions. Ratings assume clean, properly dried substrates and appropriate processing parameters.
Compatibility Rating Definitions
A — Compatible without treatment: Cohesive failure achievable in standard overmolding conditions without adhesion promoters or surface preparation. Suitable for structural bonds.
B — Compatible with process control: Adequate adhesion achievable when processing parameters (mold temperature, substrate drying, transfer time) are tightly controlled. Cohesive failure possible but process-sensitive.
C — Requires adhesion promotion: Standard process produces adhesive failure. Silane primer, tie-layer materials, or plasma treatment required for structural adhesion.
D — Not compatible without major intervention: Poor natural affinity. Specialized etching, corona treatment, or complete reformulation required. Not recommended for new designs.
ABS (Acrylonitrile-Butadiene-Styrene) — Surface Energy: 38–42 mN/m
| Elastomer | Rating | Notes |
|---|---|---|
| TPU (ether-based) | A | Strong natural affinity; cohesive failure without primers; widest process window |
| TPU (ester-based) | A | Higher initial bond strength; avoid in humid service environments |
| SEBS | A | Styrenic end-block compatibility; mold temp >60°C required |
| SBS | B | Bonds well; UV/thermal degradation limits to protected, short-life applications |
| COPE | C | Limited affinity for ABS; adhesion promoter required |
| PEBA | C | Amide chemistry not matched to ABS; tie-layer required |
| TPV | C | Inconsistent without coupling agent or surface treatment |
| ### Polycarbonate (PC) — Surface Energy: 42–46 mN/m | ||
| Elastomer | Rating | Notes |
| — | — | — |
| TPU (ether-based) | A | Strong affinity; CSC risk requires PC-screened formulation; hydrolysis resistant |
| TPU (ester-based) | B | Higher initial bond strength; CSC risk higher; avoid in humid service |
| COPE | A | Ester-to-ester compatibility; requires mold temp >75°C; high-temperature capable |
| SEBS | C | Inconsistent without adhesion promoter or tie-layer; UV stable |
| TPV | D | Poor adhesion without plasma treatment or COPE tie-layer |
| PEBA | D | Not matched to PC surface chemistry |
| ### PA6 and PA66 (Nylon 6/6.6) — Surface Energy: 40–44 mN/m (dry-as-molded) | ||
| Elastomer | Rating | Notes |
| — | — | — |
| TPU (ether-based) | A | Strong urethane-amide interaction; moisture management critical |
| TPU (ester-based) | B | Higher initial bond; degrades in humid service; use only for dry environments |
| PEBA | A | Amide-to-amide compatibility; mold temp >80°C required |
| SEBS | C | Requires silane primer for structural bonds |
| TPV | C | Requires surface treatment or PEBA tie-layer |
| COPE | D | Ester chemistry not matched to amide surface |
| ### PA12 (Nylon 12) — Surface Energy: 35–38 mN/m (lower amide density) | ||
| Elastomer | Rating | Notes |
| — | — | — |
| TPU (ether-based) | B/C | Reduced amide density limits urethane-amide interaction; silane primer + mechanical interlocks needed |
| PEBA | B/C | Better than SEBS; still weaker than on PA6; interlocks required |
| SEBS | D | Poor natural affinity; not recommended without major adhesion promotion |
| ### PET (Polyethylene Terephthalate) — Surface Energy: 40–44 mN/m | ||
| Elastomer | Rating | Notes |
| — | — | — |
| TPU | A | Urethane-to-ester interaction; similar to PC mechanism |
| COPE | A | Ester-to-ester compatibility; strong natural affinity |
| SEBS | C | Requires adhesion promotion |
| PEBA | C | Amide chemistry limited affinity for PET |
| ### Rigid PVC — Surface Energy: 38–42 mN/m | ||
| Elastomer | Rating | Notes |
| — | — | — |
| TPU | A | Good adhesion on rigid PVC; verify plasticizer compatibility for flexible grades |
| SEBS | B | Adequate adhesion; plasticizer migration from flexible PVC can contaminate bond over time |
| TPV | B | Reasonable compatibility; validate chemical resistance |
| ### Polypropylene (PP) — Surface Energy: 29–31 mN/m | ||
| Elastomer | Rating | Notes |
| — | — | — |
| TPO/Polyolefin-backbone TPE | A | Natural affinity through polyolefin matrix compatibility |
| SEBS (polyolefin-modified) | B | Modified SEBS with PP-compatible mid-block; standard SEBS is C |
| TPU | C | Requires plasma/flame treatment; bond strength lower than on polar substrates |
| COPE | D | No affinity for non-polar PP |
| PEBA | D | No affinity for non-polar PP |
| ### HDPE / LDPE — Surface Energy: 31–33 mN/m | ||
| Elastomer | Rating | Notes |
| — | — | — |
| TPO/Polyolefin TPE | B | Better than other TPE types; surface energy still low |
| TPU | D | Does not bond without surface activation and primer |
| SEBS | D | Poor adhesion even with treatment |
| For material pairing guidance and adhesion-promotion solutions for your specific substrate and elastomer combination, Email Us. | ||
| ### Key Takeaways from the Compatibility Chart | ||
| TPU is the most broadly compatible elastomer across polar engineering plastics (ABS, PC, PA, PET, rigid PVC). Its polar urethane chemistry finds a compatible bonding partner in most engineering thermoplastics through urethane-amide, urethane-ester, and urethane-nitrile interactions. | ||
| TPE sub-class matching to substrate chemistry is essential. SEBS for ABS; COPE for PC and PET; PEBA for PA6/PA66; polyolefin TPE for PP. Specifying the wrong sub-class produces adhesive failure regardless of process parameters. | ||
| Low-surface-energy substrates (PP, PE) require surface treatment for all elastomers except polyolefin-matched TPE grades. Surface treatment is required for any structural bond on polyolefins. | ||
| Difficult grades within families (PA12, glass-filled PA) require mechanical interlocks and primers regardless of which elastomer is selected — chemical adhesion alone is insufficient on these surfaces. | ||
| ### Beyond the Static Rating: Thermal and Process Considerations | ||
| The ratings above describe as-molded adhesion under room-temperature conditions, but two additional variables determine whether a rated bond survives its service life. First, thermal cycling introduces stress at the elastomer-substrate interface even for an “A”-rated pairing, because the two materials rarely share an identical coefficient of thermal expansion — the mechanism behind many field bond failures is explained in how CTE mismatch causes adhesive bond failure. A combination rated “A” for as-molded peel strength can still require thermal-cycling validation before it is qualified for an under-hood or outdoor application. | ||
| Second, when a project calls for adhesive bonding rather than overmolding — for repair, rework, or assemblies where the two components are fabricated separately — cure speed becomes a production variable in its own right, and the tradeoffs between fast-fixturing and slower, higher-strength chemistries are covered in which adhesive dries faster for quick repairs. Neither variable changes the base compatibility rating, but both determine whether that rating translates into a bond that survives the application’s actual service conditions. | ||
| Incure’s adhesive and coating formulations, including the Uni-Weld™ plastic bonder line, support demanding multi-material assemblies across all engineering plastic substrates, including adhesion-promotion solutions for difficult-to-bond combinations. For technical support on material selection and compatibility validation, Contact Our Team. | ||
| Visit www.incurelab.com for more information. |