Quick3D Shore A vs Shore D hardness explained
How the Shore A and Shore D durometer scales work, where they overlap, and how to read values like 85A and 60D on flexible material datasheets.
Flexible filaments and elastomeric resins are graded by hardness rather than stiffness. You will see values like 85A, 95A or 60D. These come from the Shore durometer scales. This article explains how they work and how to compare them.
Key takeaways
- Flexible materials are graded by Shore hardness, read from 0 to 100.
- Shore A suits soft, rubbery materials; Shore D suits harder elastomers and plastics.
- The same number means different things on each scale, and there is no exact conversion.
- Hardness is a surface measure; it does not replace stiffness, elongation or testing.
What a durometer measures
A durometer presses a small spring-loaded indenter into the surface of a material. The harder the material, the less the indenter sinks in. The dial or display reads from 0, for full penetration, to 100, for none. The test is quick and simple, which is why it is so widely used for rubbers and soft plastics.
Good to know
The main standards are ASTM D2240 and ISO 7619 (ISO 868 covers plastics). They work the same way. The reading time matters: a value taken instantly is higher than one taken after a few seconds, because soft materials keep yielding under the indenter.
Two scales, two indenters
- Shore A uses a blunt indenter and a lighter spring. It suits soft, rubbery materials.
- Shore D uses a sharp, pointed indenter and a stronger spring. It suits harder elastomers and rigid plastics.
Because the indenter and spring are different, the same number means different things on each scale. 60A is soft. 60D is firm.
60A
Shore A scale: blunt indenter, lighter spring. Soft.
60D
Shore D scale: sharp indenter, stronger spring. Firm.
Where the scales overlap
The two scales overlap around the top of Shore A and the bottom of Shore D. Very roughly, the high 90s on the A scale sit in the same region as the 40s on the D scale. The standards advise switching scales near the ends: above about 90A, measurements become less sensitive and the D scale is preferred; below about 20D, the A scale is better.
Watch out
There is no exact conversion. The two scales respond differently to different materials, so published conversion charts are approximate. If two materials are graded on different scales, compare them with care.
Everyday reference points
These are rough, general examples to build intuition:
| Feel | Example | Scale |
|---|---|---|
| Very soft, stretchy | Rubber band | Low Shore A |
| Firm but flexible | Shoe sole | Mid to high Shore A |
| Hard, slightly flexible | Skateboard wheel | Top of Shore A, bottom of Shore D |
| Rigid | Hard hat | Shore D |
Why flexible TPU and resins are graded on A
Most flexible 3D-printing materials are rubbery. Their stiffness is low, and a tensile modulus alone does not tell you how they feel or how they will seal, grip or cushion. Hardness on the Shore A scale gives a quick, intuitive measure that designers of gaskets, grips and bumpers already know.
Our catalog lists 31 TPU materials and 31 flexible resins. Most are graded on Shore A. Firmer TPUs are sometimes given on both scales, with an A reading and a D reading side by side.
- Filamen 2415–2,000
- Resin 3035–391
- Serbuk 8280–440
Bar = terendah hingga tertinggi, titik = median. 62 bahan, terus daripada pangkalan data kami. Skala log.
Good to know
We chart elongation here rather than hardness, because the catalog mixes Shore A and Shore D readings. Check the letter on each material page.
How to read “85A” vs “60D”
- The letter tells you the scale. Always read it first.
- On the A scale, lower is softer. An 85A TPU is noticeably softer and more flexible than a 95A one, and usually harder to print because it buckles in the extruder.
- On the D scale, the material is already firm. 60D is far harder than 85A.
- A value with no letter is ambiguous. Check the source datasheet.
- A range such as “80–85A” reflects batch variation or cure conditions. Design to the end that matters for your part.
Printing soft materials
Hardness also hints at how a material prints:
- Harder TPUs, around the top of the A scale, print on most machines with modest speed reductions.
- Softer TPUs are more likely to buckle or jam in the extruder. A direct-drive extruder with a constrained filament path helps, along with slower speeds and reduced retraction.
- Flexible resins need careful support placement and gentle handling before post-cure, when they are at their weakest.
Measured on a test plaque, not your part
Durometer tests use a flat specimen of a minimum thickness, often built up from stacked layers. A thin printed wall, a curved surface or a part with infill will read differently. To check a printed part, measure a solid test plaque printed with the same settings, at least as thick as the standard requires.
Hardness and stiffness
Harder elastomers are generally stiffer, but hardness is not a substitute for modulus. Hardness describes how the surface resists a small indenter. Stiffness describes how the whole part resists bending or stretching. The geometry of your part often matters more: a thick 85A pad can feel firmer than a thin 95A strap. For flexible parts that must bend a set amount under a known load, test the part itself, or a simple strip of the same thickness, rather than relying on hardness alone.
What hardness does not tell you
Shore hardness is a surface measurement. Two materials with the same hardness can differ in tear strength, elongation, rebound and how they recover after compression. For a gasket, check compression set if the sheet gives it. For a living part like a strap, check elongation at break and test the part in use. Printed infill also changes how soft a part feels: a 95A TPU printed at low infill can feel much softer than the solid material.
For more on reading datasheets, see how to read a TDS and Shore hardness.
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