Shore A vs Shore D TPE: When Your Part Needs to Be Rigid
A thermoplastic elastomer at 40 Shore D is harder than one at 90 Shore A, despite the smaller number. Shore A and Shore D are separate durometer scales, and treating the readings as one continuous ranking is one of the more common specification errors in elastomer selection. This guide explains the difference and when a rigid Shore D grade is the right answer.
Key takeaways
- Shore A and Shore D use different indenters and different loads. The numbers are not on a common scale.
- The Shore A scale saturates near its top; above roughly 90 Shore A it stops discriminating well, which is where Shore D takes over.
- There is no reliable universal conversion between the scales - published charts are polymer-dependent approximations.
- Shore D TPE behaves closer to a flexible plastic than a rubber: it carries load and holds shape while retaining impact resistance.
- The three Shore D grades in this catalogue are all UV and heat stabilised extrusion compounds.
Why there are two scales
A durometer measures how far a standardised indenter penetrates a material under a defined force. Shore A uses a relatively blunt indenter and a lighter spring, which resolves differences well among soft, rubbery materials. Push it into something genuinely rigid and the reading crowds into the high nineties, where small differences in the number stop corresponding to meaningful differences in the material.
Shore D solves that with a sharper indenter and a higher force. It is designed for the hard end of the range, so it resolves rigid materials the way Shore A resolves soft ones. The two overlap somewhere in the middle, but a reading on one scale cannot be read as a reading on the other.
What that means practically
If you specify "40 durometer TPE" without the scale, you could receive either a soft, compliant compound that compresses under thumb pressure, or a rigid one you could not deform by hand. Those are entirely different materials for entirely different parts.
This is why the FARRPRENE catalogue lists Shore A grades first and Shore D grades separately after them, each ordered within its own scale, rather than merging the numbers into a single ranking.
The Shore D grades in this range
| Grade | Hardness | Tensile | Elongation | Specific gravity | MFI 230°C | Notes |
|---|---|---|---|---|---|---|
| FARRPRENE EF400DV | 40 Shore D | 12 MPa | >850% | 1.220 | 8.1 | UV and heat stabilised, silky touch |
| FARRPRENE EF401DV | 40 Shore D | 17.4 MPa | >750% | 1.094 | 5.5 | UV and heat stabilised |
| FARRPRENE EF520DV | 52 Shore D | 18.5 MPa | >750% | 1.108 | 2.7 | UV and heat stabilised, silky touch |
Two things stand out. First, tensile strength: FARRPRENE EF520DV publishes 18.5 MPa, the highest figure in the catalogue and roughly three times what a typical mid-range Shore A grade delivers. Second, elongation stays high - above 750% on all three - so these are still elastomers, not rigid plastics. They stretch and recover; they simply resist indentation far more.
All three are extrusion grades with low melt flow (2.7 to 8.1 g/10 min at 230°C), which suits stable profile geometry, and all three carry both UV and heat stabilisation.
When to choose Shore D over hard Shore A
Move to Shore D when the part must hold its shape under sustained load rather than seal or cushion. Rigid extruded profiles, structural trim, edging and semi-rigid protective sections are the typical cases. If the part's job is to compress and recover - a gasket, a grip, a damping pad - stay on the Shore A scale, where even the hardest grades such as FARRPRENE EF902AV at 90 Shore A remain meaningfully compliant.
A useful test: if you would be disappointed by the part deforming under hand pressure, you are probably looking for Shore D.
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
Is 40 Shore D harder than 90 Shore A?
Yes, considerably. They are different durometer scales measured with different indenters and loads. The Shore A scale is designed for soft rubbery materials and compresses its resolution near the top of its range; Shore D takes over for harder materials. A 40 Shore D compound is a rigid material, whereas 90 Shore A is still a firm elastomer.
How do I convert Shore A to Shore D?
You cannot do it reliably. Conversion charts exist but they are approximations that depend on the specific polymer, so a converted value should never be used as a specification. If both scales matter to your design, measure or specify on the scale you actually intend to control.
Are Shore D TPE grades still flexible?
Yes, though far less compliant than Shore A grades. The three Shore D compounds in this catalogue all publish elongation at break above 750%, so they stretch and recover substantially. They resist indentation and hold their shape under load, which is what distinguishes them from the softer range.
What are Shore D TPE grades used for?
Rigid extruded profiles, structural trim, edging and semi-rigid protective sections - parts that need to hold their geometry under load while retaining impact resistance. They are less suited to sealing and cushioning, where a compliant Shore A grade recovers better under compression.
Why are all the Shore D grades extrusion grades?
In this catalogue they are formulated for profile extrusion, with low melt flow between 2.7 and 8.1 g/10 min at 230C to hold profile geometry between the die and the cooling line. If you need a rigid grade for injection moulding, contact us to discuss developing one.
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
- Choosing a TPE for Profile Extrusion
- Why Hardness Does Not Predict TPE Strength
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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