Hardness measures resistance to indentation. Tensile strength measures resistance to being pulled apart. They are different properties, and in thermoplastic elastomers they are only loosely related. Across the 46 Shore A grades in this catalogue the statistical correlation between hardness and tensile strength is 0.57 - a weak relationship, not a rule you can design against.
Key takeaways
- Correlation between Shore A hardness and tensile strength across 46 grades: 0.57. Weak.
- At 90 Shore A, one grade publishes 17.5 MPa tensile and another 5.5 MPa - a threefold difference at identical hardness.
- Formulation, not hardness, drives strength: base polymer, oil loading, filler type and polymer molecular weight all move tensile independently.
- Elongation at break matters as much as tensile for parts that stretch in service.
- Read tensile, elongation and hardness as three separate requirements.
The data
If hardness predicted strength, plotting one against the other across a catalogue would give a tight line. It does not. Here are the grades at the top of the Shore A range:
| Grade | Hardness | Tensile | Elongation | Process |
|---|---|---|---|---|
| FARRPRENE EF902AV | 90 Shore A | 17.5 MPa | >650% | Extrusion |
| FARRPRENE IF900A | 90 Shore A | 5.5 MPa | >800% | Injection |
| FARRPRENE IF901AS | 90 Shore A | 5.5 MPa | >500% | Injection |
Three grades at exactly the same hardness. One is more than three times stronger in tension than the other two. A specification that says "90 Shore A TPE" has not constrained strength at all.
The same pattern appears lower down the range. At 75 Shore A the tensile figures run from 3.5 MPa (FARRPRENE IF750AS) to 10 MPa (FARRPRENE EF753AV), a factor of nearly three. At 45 Shore A they run from 3.5 to 7 MPa.
Why the two properties decouple
Hardness in a TPE is dominated by the ratio of hard styrenic domains to soft mid-block and plasticising oil. Add oil and the compound gets softer. Tensile strength depends on rather different things: the molecular weight of the polymer, the styrene content, the type and loading of filler, and how well the phases are dispersed.
A compounder can hold hardness constant while moving tensile strength substantially by changing the base polymer or the filler system. That is exactly what a catalogue of 49 grades represents - different answers to different requirements, several of which happen to land on the same durometer reading.
What to specify instead
Treat hardness, tensile strength and elongation as three independent requirements, and add melt flow as a fourth for processability:
- Hardness - how the part feels and how it behaves under indentation or compression.
- Tensile strength - the stress the part can carry before failure. Matters for straps, seals under tension, and anything that will be pulled.
- Elongation at break - how far it stretches before failing. A high-tensile, low-elongation compound can still be the wrong choice for a part that must stretch over an assembly.
- Melt flow - whether it will run on your tool at all.
Elongation deserves particular attention. FARRPRENE IF901AS publishes >500% elongation while FARRPRENE IF900A publishes >800%, both at 90 Shore A. For a part that stretches over a boss during assembly, that difference decides whether it survives.
A practical selection order
Start with process, since it halves the catalogue. Then set hardness from the feel and compression requirement. Then filter on tensile and elongation against the mechanical duty. Then check the base polymer against the service environment. The grade comparison table lists all four properties for every grade in one place.
All values quoted are typical average values from a limited sample set, not a formal specification. Request the signed datasheet for current values.
Scope note. The guidance on this page is based on published mechanical properties - hardness, tensile strength, elongation, melt flow, specific gravity, base polymer and stabilisation. Food contact, skin contact, biocompatibility, flame retardancy, halogen-free formulation and electrical performance are not characterised in the public catalogue and require a separately qualified compound and testing. Contact us to qualify a grade against any of those.
Frequently Asked Questions
Does harder TPE mean stronger TPE?
No. Hardness measures indentation resistance; tensile strength measures resistance to being pulled apart. Across the 46 Shore A grades in this catalogue the correlation is only 0.57, and three grades at 90 Shore A publish tensile figures ranging from 5.5 to 17.5 MPa.
What tensile strength should I specify for a TPE part?
It follows from the mechanical duty, not from the hardness. Work out the peak stress the part will carry in service, apply your safety factor, and filter grades on tensile strength independently of the hardness you need for feel or sealing. Check elongation at break at the same time.
Why do two grades at the same hardness have different strengths?
Because hardness is set largely by the ratio of hard styrenic domains to soft mid-block and oil, while tensile strength depends on polymer molecular weight, styrene content and the filler system. A compounder can hold hardness constant and move tensile strength substantially by changing those.
Is elongation at break more important than tensile strength?
For parts that stretch in service or during assembly, often yes. A compound can be strong in tension but fail early if it does not elongate enough to accommodate the deformation. Both figures are published for every grade in this range; read them together.
Which is the strongest TPE grade in the FARRPRENE range?
On published tensile strength, EF520DV at 18.5 MPa, followed by EF902AV at 17.5 MPa and EF401DV at 17.4 MPa. Two of those three are Shore D grades, which is consistent with rigid compounds carrying more tensile load than soft ones - but note that within the Shore A range the relationship is much weaker.
Related guides
- TPE Shore Hardness: A Selection Guide From 15 Shore A to 52 Shore D
- How to Choose a TPE Grade: A Specifier's Guide
- Filled vs Unfilled TPE: What Specific Gravity Tells You
- Shore A vs Shore D TPE: When Your Part Needs to Be Rigid
About the FARRPRENE range
FARRPRENE is the thermoplastic elastomer (TPE) compound range of Farr Polychem FZCO, a polymer compounder based in Jebel Ali Free Zone, Dubai, United Arab Emirates, supplying the UAE, the wider MENA region and Europe. The range covers injection moulding and extrusion compounds from soft gel-like Shore A grades through rigid Shore D grades, in unfilled translucent and filled natural variants, colour-matchable to a customer reference, with free samples and technical datasheets available on request. Browse the full grade catalogue, see every grade side by side on the comparison table, or request a sample.
FARRPRENE GRADES
Grades commonly specified for industrial applications
| GRADE | HARDNESS | TENSILE (MPa) | TYPICAL USE |
|---|---|---|---|
| IEU150AInjection / Extrusion / Unfilled | 15 Shore A | 3 | Vibration-damping pads and soft mounts |
| IF752AInjection / Filled | 75 Shore A | 5.5 | Bushings, spacers and wear components |
| IF900AInjection / Filled | 90 Shore A | 5.5 | Hard bushings and near-rigid flexible parts |
Typical average values from a limited sample set; not a formal specification. Request the signed datasheet for current values.
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