Shore A and Shore D are two hardness scales used to describe how much a material resists local indentation. In filament terms, Shore A usually appears on flexible materials such as TPU and TPE, while Shore D is more common on rigid plastics such as PLA, PETG, ABS, ASA, nylon, and PC. The number matters, but the letter matters just as much.
- What the Shore Number Measures
- Hardness Is Not the Same as Strength
- How Shore A Reads Flexible Filament
- What a Higher Shore A Value Usually Suggests
- How Shore D Reads Rigid Filament
- What a Higher Shore D Value Usually Suggests
- Why 95A Is Not the Same as 95D
- Scale Feel Without Treating It as a Conversion
- Material Examples from Filament Datasheets
- Hardness, Flexibility, and Printed Geometry
- Thin Parts Can Feel Softer Than Their Rating
- Thick Flexible Parts Can Feel Firmer Than Expected
- How the Rating Connects to Filament Behavior
- Filament Behavior by Scale Area
- Where Each Scale Makes More Sense
- Common Misreadings of Shore A and Shore D
- Reading the Number Without the Letter
- Treating Hardness as Heat Resistance
- Comparing Different Brands Too Literally
- Ignoring the Printed-Part Test Conditions
- Reading a Filament Datasheet Hardness Line
- Shore A vs Shore D in Plain Material Terms
- Resources Used
| Comparison Point | Shore A | Shore D |
|---|---|---|
| Main filament use | Flexible and semi-flexible filament families such as TPU, TPE, soft copolyesters, and rubber-like materials. | Rigid or semi-rigid filament families such as PLA, PETG, ABS, ASA, nylon, PC, and many filled blends. |
| Scale style | 0–100 on the A scale. A higher number means the indenter enters the material less. | 0–100 on the D scale. A higher number also means less indentation, but the durometer is different. |
| Typical feel in printing | More elastic, grippy, bendable, and compressible as the number moves downward. | More plastic-like, crisp, and shape-holding as the number moves upward. |
| Common example range | Flexible filaments often appear around 60A–98A, depending on formulation and brand. | Rigid filaments often appear around the 70D–85D area in many datasheets, depending on polymer and additives. |
| Overlap zone | High Shore A values can overlap with lower Shore D readings. | Low to mid Shore D readings can describe materials that still have some flex. |
| Best use of the value | Comparing flexible filament grades with similar chemistry. | Comparing harder plastic filaments and stiff blends with similar test conditions. |
| Main reading mistake | Thinking 95A is nearly the same as 95D. | Thinking 45D must be softer than 95A just because the number is lower. |
This Shore A and Shore D comparison uses filament datasheets plus trusted standards references; the values show scale trends, while real printed parts can vary with formulation, print settings, geometry, and test conditions.
- Indentation hardness
- Separate durometers
- 0–100 scale
- Flexible TPU/TPE
- Rigid PLA/PETG/ABS
What the Shore Number Measures
A Shore reading measures how far a standardized indenter pushes into a material under a defined force. Harder materials allow less penetration. Softer materials allow more. That is the center of the test: not color, not surface gloss, not “strength” in the everyday sense.
ASTM D2240 describes durometer hardness as a penetration-based test and notes that different durometer types do not have a simple direct relationship with one another. That matters for filament because Shore A and Shore D are not two labels for the same ruler.[a]
ISO 868 also treats Shore hardness as an indentation method for plastics and ebonite, using type A durometers for softer materials and type D durometers for harder materials. The reading may be taken immediately or after a stated time interval, so a clean datasheet should tell you the method behind the number.[b]
Hardness Is Not the Same as Strength
A high Shore D number can suggest a firm surface, yet it does not automatically tell you tensile strength, impact behavior, heat resistance, or layer adhesion. A soft TPU can stretch far before break. A rigid PLA can feel hard but bend only a little before yielding. Different property.
- Hardness
- Resistance to a small indenter pressing into the surface.
- Flexibility
- How easily a printed shape bends under load.
- Tensile modulus
- How stiff a material behaves in a tensile test.
- Elongation at break
- How far the material can stretch before it breaks.
- Layer adhesion
- How well printed roads bond across the layer structure.
How Shore A Reads Flexible Filament
Shore A is the scale most people see when reading about flexible filament. TPU marked 95A is usually much easier to feed and shape-hold than a very soft 60A or 70A grade, while still feeling more elastic than a rigid PLA or PETG part.
The A scale is useful because many flexible filaments live in the same broad family: elastomeric, bendable, and more compressible than rigid thermoplastics. A number such as 85A, 90A, or 95A gives a first clue about surface firmness and handling behavior.
What a Higher Shore A Value Usually Suggests
- Less surface indentation under the same durometer test.
- More shape-holding feel compared with lower-A flexible grades.
- Less rubbery compression in the filament path.
- A firmer grip surface, tire, bumper, sleeve, seal-like shape, or wearable part.
This does not mean high-A TPU becomes rigid. It still belongs to a flexible material family. The part geometry can make it feel much softer or firmer than the small datasheet number suggests.
How Shore D Reads Rigid Filament
Shore D is more common for harder plastics. PLA, PETG, ABS, ASA, nylon, PC, and many fiber-filled blends are usually discussed on the D scale because a Shore A indenter can reach the upper end of its useful range on these materials.
A rigid filament with a Shore D value around the high 70s or low 80s is not automatically “better” than a material with a slightly lower value. It may simply have a firmer surface under the durometer while showing a different balance of toughness, heat behavior, stiffness, and elongation. Hardness is one measurement.
What a Higher Shore D Value Usually Suggests
- A firmer surface under indentation.
- A more plastic-like feel in thin edges and flat faces.
- Better resistance to small surface dents compared with a softer material in the same family.
- Less rubber-like compression than Shore A flexible grades.
Why 95A Is Not the Same as 95D
The numbers can mislead. A material marked 95A is near the hard end of the Shore A scale, but 95D would be far up the hard-plastic side of the Shore D scale. Same number. Very different meaning.
Some reference charts place Shore 95A near Shore 45D as an approximate overlap point, which is helpful for orientation but not a true conversion formula.[c] The safer habit is simple: read the number and letter together, every time.
Scale Feel Without Treating It as a Conversion
High Shore A Flexible Grade firm elastomer feel
High Shore D Rigid Grade hard plastic feel
The bars are a relative visual only. They show scale position, not a lab conversion between Shore A and Shore D.
Material Examples from Filament Datasheets
Real datasheets show why the letter beside the number cannot be ignored. A flexible TPU can report both an A-scale and a D-scale hardness in the same document, while rigid filaments often list only Shore D.
| Filament Example | Hardness Data Shown | Other Datasheet Values | What It Shows |
|---|---|---|---|
| UltiMaker TPU 95A | 96 Shore A and 48 Shore D | XY tensile modulus 67 MPa; XY elongation at break greater than 560%. | A flexible filament can sit near the hard end of Shore A while also having a lower Shore D reading.[d] |
| Prusament PLA | 81 Shore D | Density 1.24 g/cm³; heat deflection temperature 55 °C at 0.45 MPa and 1.80 MPa. | PLA is commonly treated as a rigid filament, so Shore D is the more natural scale.[e] |
| Prusament PETG V0 | 79 Shore D | Density 1.27 g/cm³; heat deflection temperature 74 °C at 1.80 MPa. | PETG can have a Shore D value close to PLA while still behaving differently in toughness and thermal response.[f] |
Hardness, Flexibility, and Printed Geometry
Printed geometry can change the feel of a part more than many people expect. A 95A TPU sheet with thick walls and high infill may feel firm in the hand, while a thin lattice from a higher-D material may flex under finger pressure because the shape allows it. The material gives the baseline; the design gives the movement.
For that reason, Shore hardness is best read as surface indentation resistance. It is not a full prediction of part softness. Wall count, infill pattern, part thickness, print orientation, and temperature exposure all affect the final feel.
Thin Parts Can Feel Softer Than Their Rating
A thin PLA tab can bend even though PLA carries a high Shore D rating. The surface is still hard under the indenter, but the slender geometry lowers bending resistance. Small hinges, clips, and tabs make this clear.
Thick Flexible Parts Can Feel Firmer Than Expected
A thick TPU bumper can feel firm even when the material is still elastomeric. More material under the load means more resistance to deformation. Same Shore value, different part feel.
How the Rating Connects to Filament Behavior
Hardness affects more than touch. It also relates to how the filament behaves as a strand before it becomes a part. Lower Shore A materials are more compressible in the feed path, while higher Shore D materials tend to keep a rounder, more stable shape under the drive gears.
Filament Behavior by Scale Area
- Lower Shore A: more rubber-like compression, more bend, softer contact feel.
- Higher Shore A: firmer flexible behavior, less squash under local load.
- Lower Shore D: semi-rigid or hard-elastomer behavior, depending on chemistry.
- Higher Shore D: firm plastic feel, better shape-holding in small details.
Where Each Scale Makes More Sense
| Use Case | More Useful Scale | Reason |
|---|---|---|
| TPU grip, bumper, sleeve, tire, flexible foot, or soft spacer | Shore A | The part behavior is elastomer-like, so the A scale gives better separation between soft and firm flexible grades. |
| PLA display part, fixture, jig body, bracket shell, or dimensionally firm model | Shore D | The material behaves more like a hard plastic, so the D scale gives a better indentation range. |
| Semi-flexible copolyester or very firm TPU | Shore A and Shore D may both appear | The material may sit in the overlap zone, where one scale alone can hide part of the story. |
| Filled PLA, carbon fiber blends, glass fiber blends, and stiffer engineering filaments | Shore D | The surface and body behavior are usually closer to rigid plastics than rubber-like filaments. |
Common Misreadings of Shore A and Shore D
Reading the Number Without the Letter
“95” alone tells you almost nothing. It might mean a firm TPU if the label says 95A, or a much harder plastic-like material if the label says 95D. The letter is part of the value.
Treating Hardness as Heat Resistance
Shore hardness does not replace HDT, Vicat softening temperature, glass transition data, or long-term temperature notes. A material can feel hard at room temperature and still soften earlier than another material with a similar Shore value.
Comparing Different Brands Too Literally
Two filaments with the same Shore rating can print and feel slightly different because polymer grade, plasticizer content, fillers, pigments, moisture history, and test preparation can shift results. The Shore number is useful. It is not the whole datasheet.
Ignoring the Printed-Part Test Conditions
Some datasheets measure raw material. Some measure printed specimens. Some state orientation, infill, nozzle, layer height, and conditioning; others provide less detail. A hardness line with method notes is more useful than a bare number.
Reading a Filament Datasheet Hardness Line
- Keep the number and letter together: 95A, 48D, 81D.
- Check whether the method says ASTM D2240, ISO 868, ISO 7619, or another related hardness method.
- Look for whether the sample is raw filament, molded material, or a printed specimen.
- Compare materials from the same family first, such as TPU-to-TPU or PLA-to-PLA.
- Use tensile modulus, elongation, HDT, and impact data beside hardness for a fuller material picture.
The cleanest comparison is not “which number is bigger?” It is “which scale was used, on what sample, under which method, and with what other mechanical data?” That reading habit avoids most hardness confusion.
Shore A vs Shore D in Plain Material Terms
Shore A belongs closest to the flexible side of filament selection. It describes how soft or firm an elastomer-like material feels under an indentation test. Shore D belongs closest to the rigid side. It describes hard plastics and semi-rigid materials with a different durometer setup.
For 3D printing, the most useful reading is practical and narrow: Shore A helps compare flexible filament firmness; Shore D helps compare rigid filament surface hardness. When a material sits near the overlap zone, both values can be useful, but they should still be treated as separate scale readings.
Resources Used
- [a] ASTM D2240 — Standard Test Method for Rubber Property—Durometer Hardness
- [b] ISO 868:2003 — Plastics and ebonite — Determination of indentation hardness by means of a durometer (Shore hardness)
- [c] Smooth-On — Durometer Shore Hardness Scale
- [d] UltiMaker TPU 95A — Technical Data Sheet
- [e] Prusament PLA by Prusa Polymers — Technical Datasheet
- [f] Prusament PETG V0 by Prusa Polymers — Technical Datasheet
