Shore A vs Shore D Filament: Hardness Ratings Explained

Shore A and Shore D are two hardness scales used to describe how much a material resists local indentation. In filament terms, Shore A appears most often on flexible materials such as TPU and TPE, while Shore D is common on rigid plastics such as PLA, PETG, ABS, ASA, nylon, and PC. Very firm TPU can also sit on the Shore D scale, with 68D TPU now providing a useful 3D-printing example. The number matters, but the letter matters just as much.

• Indentation hardness
• Separate durometers
• 85A / 90A / 95A
• 68D TPU
• Flexible to firm TPU
• Rigid plastics

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. The test measures indentation hardness rather than tensile strength, impact resistance, heat resistance, or overall part stiffness.

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. For filament, this means 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 the test method and sample conditions belong beside the hardness number.[b]

Hardness Is Not the Same as Strength

A high Shore D number can indicate 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 breaking. A rigid PLA can feel hard while tolerating far less bending. These properties need their own measurements.

How Shore A Reads Flexible Filament

Shore A is the scale most people see when comparing flexible filament. TPU marked 95A is usually easier to feed and better at holding its shape than a very soft 60A or 70A grade, while still behaving more elastically than PLA or PETG.

The differences inside the common TPU range are useful in actual part selection. 85A, 90A, and 95A are all flexible grades, but they do not feed, compress, bend, or recover in exactly the same way.

Bambu Lab’s current TPU range includes TPU 85A and TPU 90A, positioning 85A toward softer shock-absorbing applications and 90A toward firmer parts such as shoe soles and RC tires.[g] Both remain softer and more compressible than the firm’s 95A and 68D options.

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. A 95A TPU still belongs to a flexible material family, and printed geometry can make the finished part feel much softer or firmer than the hardness number alone suggests.

How Shore D Reads Harder Materials

Shore D is common for harder plastics. PLA, PETG, ABS, ASA, nylon, PC, and many fiber-filled blends are normally discussed on the D scale because a Shore A durometer reaches the upper end of its useful range on materials this firm.

Shore D is not restricted to rigid plastics. A hard elastomer can also be measured on this scale. Bambu Lab’s TPU for AMS is rated at 68D, giving current filament users a direct example of TPU that sits on the Shore D side while retaining TPU flexibility and durability.[i]

A 68D TPU therefore should not be grouped with PLA merely because both use Shore D measurements. Polymer chemistry still determines how the material stretches, recovers, bonds, and handles repeated deformation. The Shore value tells you how resistant its surface is to the specified indentation test.

What a Higher Shore D Value Usually Suggests

• A firmer surface under indentation.
• Greater resistance to local compression than softer grades in the same material family.
• More shape-holding behavior in the filament path.
• Less rubber-like compression than ordinary Shore A flexible grades.

A rigid filament with a Shore D value around the high 70s or low 80s is not automatically better than a material with a lower value. A 68D TPU and an 81D PLA serve very different jobs even though both hardness values are reported on the same scale.

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, while 95D would sit far up the hard-material side of the Shore D scale. The identical number does not make the materials equally hard.

Some reference charts place Shore 95A near Shore 45D as an approximate overlap point, which is useful for orientation but not a true conversion formula.[c] A value should therefore be kept together with its scale letter.

The 2026 TPU Range: 85A, 90A, 95A HF, and 68D

Current TPU product lines make hardness more useful than a simple “soft versus rigid” split. Bambu Lab now sells TPU across 85A, 90A, 95A HF, and 68D TPU for AMS. These grades differ not only in indentation hardness but also in feed-path behavior, supported material systems, print speed, and the kinds of parts they suit.[g][h][i]

The 68D product is especially useful for understanding the scales. It is still TPU, but it is firm enough that Shore D is the more suitable durometer range. Its higher hardness also makes the filament strand less prone to buckling and compression inside an automated feed system than softer 85A, 90A, or 95A TPU.

Bambu’s current TPU printing information separates softer TPU from TPU for AMS for this reason. TPU 85A and 90A need a feed path suited to very flexible filament, while the 68D formulation is specifically designed around automated material handling.[j]

68D Does Not Mean TPU Has Become Rigid

TPU for AMS feels far firmer than ordinary 85A, 90A, or 95A flexible filament, but its Shore D rating does not change the polymer family into PLA or PETG. It retains elastomeric behavior while resisting indentation and feed-path compression much more strongly than softer TPU.

That combination explains why 68D can suit parts such as durable tags, protective elements, flexible fixtures, multicolor parts, and other prints where some deflection and recovery are useful but a soft rubber-like feel is not required.

High-Flow TPU Changes Print Speed Without Changing the Shore Scale

Hardness and flow rate are separate properties. Two filaments can both be called 95A TPU while behaving very differently when pushed through the hotend at high volumetric flow. This is where high-flow TPU differs from a hardness comparison alone.

Bambu Lab lists TPU 95A HF with a 12 mm³/s maximum volumetric speed and describes it as printing up to three times faster than its regular TPU 95A reference.[h] The manufacturer comparison lists 3.6 mm³/s for the regular 95A reference, so the HF formulation is intended to sustain much greater material throughput while remaining in the same 95A hardness class.

The 12 mm³/s figure is a manufacturer rating rather than a guarantee that every model should be printed at that limit. TPU remains sensitive to moisture, feed resistance, hotend conditions, retraction, geometry, and sustained extruder pressure. A small detailed model may also spend little time near maximum flow even when the filament can support it.

This follows the same material-flow principle covered in High-Speed Filament vs Standard Filament: linear speed in mm/s is only part of the picture. Layer height, line width, nozzle size, and speed together determine how many cubic millimeters of polymer the hotend must melt each second.

Material Examples from Filament Datasheets

Published material data shows why the scale letter cannot be ignored and why TPU should no longer be treated as a Shore A-only filament family. Flexible TPU can report both A and D hardness, rigid filaments usually sit on Shore D, and current hard TPU products can use Shore D while remaining elastomeric.

Hardness, Flexibility, and Printed Geometry

Printed geometry can change the feel of a part more than the hardness number suggests. A 95A TPU sheet with thick walls and high infill may feel firm in the hand, while a thin lattice made from a harder material may flex under finger pressure because the geometry allows it. Material hardness provides one property; geometry controls how that material is arranged.

Shore hardness is therefore most useful 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 remains hard under the indenter, but the slender geometry lowers bending resistance. Small hinges, clips, and tabs show this clearly.

Thick Flexible Parts Can Feel Firmer Than Expected

A thick TPU bumper can feel firm even when the material is elastomeric. More material under the load increases resistance to deformation. The Shore rating can remain unchanged while the finished part feels very different.

How the Rating Connects to Filament Feeding

Hardness affects more than touch. It also relates to how the filament behaves as a strand before reaching the nozzle. Lower Shore A materials are more compressible in the feed path, while firmer materials resist buckling and retain a rounder shape under drive gears.

This feed-path effect is one reason Bambu’s 68D TPU for AMS can be handled through AMS and AMS Lite while the softer 85A and 90A grades are not listed for those normal automatic feed paths.[g][i] The distinction comes from filament handling as well as finished-part feel.

Where Each Scale Makes More Sense

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 an extremely hard material if it says 95D. The letter is part of the value.

Assuming Every Shore D Filament Is Rigid

Bambu TPU for AMS is a useful counterexample. Its 68D rating sits on the Shore D scale, yet the material remains TPU and retains flexibility. Shore D tells you the indentation test range, not the polymer family.

Assuming a Higher Hardness Rating Prints Faster

A harder TPU strand may feed more easily, but Shore hardness does not specify melt flow. Bambu TPU 95A HF demonstrates the difference: its speed claim comes from a high-flow formulation, not from changing the nominal hardness above 95A.[h]

Treating Hardness as Heat Resistance

Shore hardness does not replace HDT, Vicat softening temperature, glass transition data, or long-term temperature information. 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 different because polymer grade, additives, pigments, moisture history, and test preparation can shift material behavior. A 95A label does not guarantee the same flow limit, elongation, rebound, or surface feel from every manufacturer.

Ignoring the Test Conditions

Some datasheets measure raw material. Some measure molded specimens or printed samples. Some state orientation, infill, nozzle, layer height, and conditioning; others provide less detail. Hardness values are most useful when the test method and specimen conditions are also available.

Reading a Filament Datasheet Hardness Line

1. Keep the number and letter together: 85A, 95A, 48D, 68D, 81D.
2. Check whether the method says ASTM D2240, ISO 868, ISO 7619, or another related hardness method.
3. Look for whether the sample is raw material, molded material, or a printed specimen.
4. Compare materials from the same family first, such as 85A TPU with 90A TPU or one 95A TPU with another.
5. Do not use hardness to infer maximum print speed; check volumetric-flow or speed data separately.
6. Use tensile modulus, elongation, HDT, impact data, and feed-system compatibility beside hardness when they matter to the part.

A useful comparison keeps the scale, sample method, mechanical data, and printer requirements separate. This avoids treating a 68D TPU like an ordinary rigid plastic or assuming that two 95A TPU products must print at the same speed.

Shore A vs Shore D in Filament Terms

Shore A remains the normal scale for soft and medium-firm flexible filament. It separates materials such as 85A, 90A, and 95A TPU according to indentation hardness. Shore D is the more suitable scale once materials become much firmer, including rigid plastics and hard elastomers such as 68D TPU.

For 3D printing, Shore A is useful for comparing flexible TPU firmness, while Shore D covers harder plastics and very firm TPU grades. The 2026 TPU market also shows why hardness should be kept separate from print throughput: 95A HF can flow much faster than standard 95A, while 68D TPU can solve feed-system problems by being much firmer without becoming an ordinary rigid thermoplastic.

Resources Used

1. [a] ASTM D2240 — Standard Test Method for Rubber Property—Durometer Hardness
2. [b] ISO 868:2003 — Plastics and ebonite — Determination of indentation hardness by means of a durometer (Shore hardness)
3. [c] Smooth-On — Durometer Shore Hardness Scale
4. [d] UltiMaker TPU 95A — Technical Data Sheet
5. [e] Prusament PLA by Prusa Polymers — Technical Datasheet
6. [f] Prusament PETG V0 by Prusa Polymers — Technical Datasheet
7. [g] Bambu Lab — TPU 85A / TPU 90A
8. [h] Bambu Lab — TPU 95A HF
9. [i] Bambu Lab — TPU for AMS, 68D
10. [j] Bambu Lab Wiki — TPU Printing Guide