For decades, engineers designing flexible components — automotive boots, cable jackets, industrial hoses — defaulted to vulcanized rubber or thermoplastic polyurethane (TPU). Both materials do many things well. But they each carry a constraint that limits where they can be specified: rubber requires vulcanization and cannot be remolded, while TPU struggles in high-temperature environments and degrades through hydrolysis when exposed to moisture or fuels over time.
TPEE Pellets has moved into the gap between those two. It processes on standard thermoplastic equipment like TPU, but its polyester-based hard segments push heat resistance, fuel resistance, and long-term dimensional stability into territory that TPU typically cannot match. Compared to rubber, it is fully recyclable, can be reprocessed, and eliminates the vulcanization step that adds cost and cycle time to rubber part production.
Figure 1 — TPEE vs. TPU vs. Rubber across five engineering-critical dimensions
The result is a material that sits in a performance band no single incumbent fully covers: flexible and recoverable like rubber, processable like TPU, and heat-resistant and chemically stable beyond what either can reliably offer. That combination is why TPEE adoption continues to expand in automotive under-hood, wire and cable, and industrial fluid-handling applications.
TPEE stands for Thermoplastic Polyester Elastomer. It is a block copolymer — a polymer chain in which two chemically distinct repeat units alternate in defined sequences called blocks. In TPEE, one block type is rigid (the "hard segment") and the other is flexible (the "soft segment"). The ratio and architecture of these segments determine every macroscopic property of the material.
The hard segments in TPEE are typically composed of polybutylene terephthalate (PBT) units — the same aromatic polyester used as an engineering thermoplastic in its own right. These segments crystallize when the melt cools, forming physical crosslinks that give TPEE its dimensional stability, elevated melting point, and resistance to solvents and hydrocarbons. Because these crosslinks are physical (crystalline) rather than covalent (as in rubber vulcanizates), they melt when the material is reheated, enabling reprocessability.
The soft segments are either polyether-based (for example, polytetramethylene ether glycol, PTMEG) or aliphatic polyester-based. These flexible chains remain amorphous at room temperature, giving the material its elastic recovery, low-temperature flexibility, and impact resilience. The choice between polyether and polyester soft segments affects hydrolysis resistance and low-temperature performance — polyether soft segments generally provide better hydrolysis resistance than polyester soft segments, which is why they are preferred in automotive fuel-system and outdoor applications.
Figure 2 — TPEE block copolymer architecture: alternating hard (PBT) and soft (polyether) segments
The TPE family is broad. TPU (Thermoplastic Polyurethane) uses urethane linkages in its hard segment; TPEE uses ester linkages. That difference may sound minor, but it has major practical consequences. Ester linkages in the PBT hard segment crystallize more perfectly and melt at a higher temperature than the urethane domains in TPU, giving TPEE its superior heat resistance. TPE (generic) and TPR (Thermoplastic Rubber) are typically softer, lower-temperature materials without the crystalline hard segment structure. Vulcanized rubber has permanent crosslinks; TPEE has reversible crystalline crosslinks — that is the root reason TPEE can be recycled and rubber cannot.
One of the most practical things a buyer or engineer can do when evaluating TPEE is learn to decode the grade naming convention. At Joysun, grade names encode the two most important specification anchors directly in the number.
Figure 4 — Grade name decoding: the first two digits = Shore D hardness, next three = melting point in °C
Using this convention: Grade 3016 = Shore D 30, melting point 160°C (approx.). Grade 5518 = Shore D 55, melting point 180°C (approx.). Grade 8218 = Shore D 82, melting point 218°C (approx.). This makes it possible to estimate a grade's performance envelope from its name alone — before even opening a data sheet.
Joysun's current high-performance TPEE lineup spans the following grades. Each links to the full technical data sheet:
| Grade | Series | Shore D | Flex Modulus (MPa) | Elongation (%) | Melting Pt (°C) | MFR (g/10min) |
|---|---|---|---|---|---|---|
| 3016 | Soft | 29 | 26 | 900 | 172 | 6 (190°C) |
| 4016 | Soft | 40 | ~80 | ~700 | ~160 | — |
| 4320 | Medium-Soft | 43 | ~100 | ~600 | ~200 | — |
| 45211T ★ | Medium-Soft | 45 | 120 | 540 | 211 | 11 (230°C) |
| 5518 | Medium-Hard | 55 | 190 | 600 | 200 | 8 (230°C) |
| 6319 | Medium-Hard | 62 | 279 | 500 | 209 | 9 (230°C) |
| 72213 | Hard | 72 | ~400 | ~400 | ~213 | — |
| 8218 | Hard | 82 | ~600 | ~200 | 218 | — |
★ 45211T highlighted — flame-retardant modified grade. Data from published Joysun technical data sheets. Approximate values indicated by ~.
TPEE is processed on standard thermoplastic equipment, which is a significant advantage over rubber. However, certain material-specific steps are essential to preserve molecular weight and achieve consistent part quality. Three processing methods dominate commercial TPEE applications.
Figure 5 — Three primary TPEE processing methods and their key parameters
Before any melt processing, TPEE pellets must be dried to remove absorbed moisture. Moisture present in the melt causes hydrolytic chain scission — a chemical reaction that irreversibly reduces molecular weight and degrades tensile strength and elongation. A dehumidifying dryer at 80–100°C for a minimum of 4 hours is standard. Higher-hardness, higher-melting-point grades may need 5–6 hours. Moisture content should target below 0.02% before processing.
Melt temperature should be set 20–30°C above the published melting point of the selected grade. For 45211T (melting point 211°C), that means a melt temperature in the range of 230–245°C. Mold temperature between 20–60°C is appropriate for most grades; the higher end of this range improves surface finish and crystallinity in thicker sections. Gate design should avoid abrupt cross-section changes to minimize localized shear heating. Because TPEE crystallizes on cooling, wall thickness uniformity is important — thick sections require longer cooling times to prevent sink marks or internal voids.
Single-screw extrusion with a compression ratio of 2.5:1 to 3:1 handles most Joysun TPEE grades effectively. A screen pack (typically 60–100 mesh) is recommended to filter gels that can form if the material is overheated locally. For cable jacketing applications, a crosshead die with precise gap control ensures uniform wall thickness. Cooling should be gradual — abrupt quenching in cold water can introduce internal stress in thicker profiles.
Blow molding is used primarily for hollow parts: automotive CV joint boots, air ducts, and bellows. Medium-hard grades with good melt strength — such as Grade 5518 or Grade 6319 — are most suitable because they form a stable parison without sagging. Parison wall thickness programming is especially important for parts with varying diameter sections.
TPEE is not a niche material. It serves several large industrial sectors, each exploiting a different subset of its property profile.
Figure 6 — TPEE application areas across four major industries with recommended Joysun grades
Automotive is the primary commercial driver for medium-hard and hard TPEE grades. Under-hood components face continuous heat exposure, fuel splash, vibration, and repeated flex cycles — conditions that eliminate many alternative materials. TPEE outperforms EPDM rubber in fuel-contact applications due to significantly lower fuel swell. CV joint boots are a canonical example: the part must flex through thousands of cycles across a wide temperature range, resist grease, and maintain its sealing geometry. TPEE delivers all of this from a single, recyclable material that can be injection molded or blow molded.
Soft to medium TPEE grades — particularly flame-retardant variants — serve as cable jacketing materials for telecommunications, industrial power distribution, and data cables. Grade 45211T was specifically developed to address wire and cable requirements: its Shore D 45 hardness provides flexibility on the cable drum, its 540% elongation prevents jacket cracking during installation, and its 211°C melting point means the jacket survives short-circuit temperature events that would compromise softer alternatives. The flame-retardant modification supports IEC and UL flame classifications without halogenated compounds.
TPEE's resistance to a broad range of chemicals, combined with its ability to be extruded to tight dimensional tolerances, makes it a competitive material for pneumatic tubing, hydraulic return lines, and chemical transfer hose covers. It competes directly with nylon (PA12) and thermoplastic polyurethane in this space, offering better UV resistance than TPU and better flexibility at low temperatures than PA12.
Grade selection is a filtering process. Working through the following parameters in sequence narrows the field to a short list, which can then be confirmed with sample testing.
Define the stiffness the application requires. Sealing elements, cable jackets, and highly flexible connectors: Shore D 29–45 (Grades 3016, 4016, 4320, 45211T). Corrugated ducts, automotive boots, coiled tubing: Shore D 46–65 (Grades 5518, 6319). Structural brackets, stiff-wall tubing, load-bearing clips: Shore D 66–82 (Grades 72213, 8218).
Two grades with the same Shore D can have different flexural modulus values. If the application involves bending loads, specify from the MPa column, not just Shore D. Grade 6319 (Shore D 62, 279 MPa) and a hypothetical Shore D 62 grade with 180 MPa will behave differently under the same bending force.
Add a minimum safety margin of 20–30°C between the maximum service temperature and the melting point. For under-hood locations reaching 130°C, the grade's melting point should be at least 160°C — and preferably above 200°C to avoid creep and dimensional change. Grade 45211T at 211°C and Grade 6319 at 209°C both provide comfortable margin for high-temperature automotive environments.
Higher MFR grades (e.g., Grade 45211T at 11 g/10 min at 230°C) are more fluid in the melt and suit high-speed extrusion and thin-wall injection molding. Lower MFR grades require more back-pressure and higher processing temperatures, which may mean equipment adjustments. Confirm your extruder or injection machine's barrel capacity and screw design can handle the selected grade's viscosity range.
If the application requires flame retardancy (cable jacketing, electronics enclosures), specify Grade 45211T or contact the Joysun technical team for custom compound options. If the part contacts specific chemicals, request a chemical compatibility data sheet before finalizing the grade — generic TPEE resistance data is not a substitute for application-specific testing.
No grade selection process substitutes for physical testing of the actual part geometry under actual service conditions. Contact Joysun via the contact page or at sale@joysunsh.com to request samples and technical support for your application development.
