Materials Guide

Flexible 3D Printing Materials: Shore Hardness, TPU Grades & Multimaterial Compatibility.

Flexible materials bend, stretch, and compress without fracturing — unlocking prosthetics, wearables, gaskets, seals, soft robotics, and impact-resistant components that rigid plastics cannot produce. Understanding shore hardness, material types, and printer compatibility is the difference between a successful flexible print and a clogged extruder.

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Why flexibility matters

Not all flexible materials are the same. A phone case at 95A Shore hardness feels nothing like a medical-grade wearable at 75A. The number on the spool — Shore hardness — determines how soft the printed part feels, how fast you can print it, whether your printer can feed it at all, and whether it can run through a multimaterial system. This guide covers the full spectrum from rigid-flex 98A to ultra-soft 60A, with specific print settings, printer compatibility matrices, and multimaterial system constraints for every grade.

60A–98A

Full printable shore hardness range for FDM flexible materials — from rubber-band soft to near-rigid

700%

Maximum elongation at break for premium TPU formulations — stretches 7× its length before snapping

15 mm/s

Minimum print speed for ultra-soft TPUs (85A and below) — patience is mandatory with flexible filaments

0

Soft TPUs that can run through a Bambu AMS without modification — 68D AMS-specific TPU is the only exception

Understanding Shore Hardness: The Number That Defines Your Flexible Print

Shore hardness is a standardized measurement of a material's resistance to indentation. A calibrated probe is pressed into the material under a fixed load, and the depth of the indent determines the hardness number. For flexible 3D printing filaments, two scales are relevant:

Shore A — The scale for soft, flexible materials: rubbers, elastomers, and flexible filaments. Values range from 0 (gel) to 100 (rigid plastic). Most TPU and TPE filaments fall between 60A and 98A.

Shore D — The scale for harder plastics. Standard PLA and ABS are in the Shore D range. Some semi-rigid TPU formulations (60D–68D) bridge both scales — they feel like stiff plastic with a slight give rather than rubber.

Shore Hardness Reference by Everyday Objects

Shore Hardness	Feels Like	Printability	Best For
60A	Gel insole, rubber band	Extremely difficult — direct drive only	Ultra-soft wearables, medical seals
75A	Shoe heel cushion, earplug	Very difficult — direct drive, 15–20 mm/s	Wearables, skin-contact parts, vibration dampening
85A	Pencil eraser, soft shoe sole	Difficult — direct drive, 15–25 mm/s	Gaskets, seals, phone cases, wearables
90A	Car tire, firm shoe sole	Moderate — direct drive preferred, 25–40 mm/s	Functional rubber parts, wheels, grips
95A	Skateboard wheel, rubber mallet	Easy — direct drive or Bowden, 40–60 mm/s	Phone cases, drone bumpers, general engineering
98A	Hard rubber, hockey puck	Easy — any printer, 30–50 mm/s	Impact-resistant parts, semi-flexible enclosures
60D–68D	Stiff plastic with slight give	Easy — AMS-compatible at 68D	Protective cases, automotive parts, multi-material prints

Key principle: Lower shore number = softer material. The printable range for direct drive FDM printers is approximately 60A to 98A. Below 60A, even well-tuned direct drive extruders struggle to maintain consistent pressure without buckling. Above 98A, the material behaves more like semi-rigid plastic and is better classified on the Shore D scale.

TPU Grades by Shore Hardness: Detailed Profiles

01 — 85A TPU: Ultra-Soft Flexibility

85A is the softest commercially viable TPU grade for FDM printing. It feels like a pencil eraser — genuinely squishy, with high grip and excellent vibration dampening. 85A parts compress easily under finger pressure and recover their shape, making them ideal for wearables, gaskets, and medical applications.

Property	Value
Shore Hardness	85A
Nozzle Temperature	220–250°C
Bed Temperature	50–60°C
Print Speed	15–25 mm/s
Retraction	Disabled (0 mm) — retraction grinds soft filament
Extruder Type Required	Direct drive only — Bowden will buckle
Elongation at Break	500–700%
Multimaterial Compatible	No — external spool only on Bambu; Prusa MMU not recommended
Leading Products	NinjaTek Chinchilla (75A), NinjaFlex (85A), Recreus Filaflex (84A)

Printing tips for 85A: Use a direct drive extruder with zero retraction. Print the first layer slow (10–15 mm/s) for adhesion. Disable or minimize cooling fan — over-cooling 85A causes poor layer adhesion and brittle parts. Store filament in a dry box with desiccant before and after printing — 85A is highly hygroscopic. Use coasting or wipe settings instead of retraction to manage stringing.

02 — 90A TPU: Medium-Soft Functional Flexibility

90A sits between the ultra-soft 85A and the ubiquitous 95A. It offers genuinely rubbery feel with somewhat easier printability than 85A. However, 90A is rarely stocked by major manufacturers because tuned 95A parts with adjusted infill and wall settings can approximate 90A feel in most applications.

Property	Value
Shore Hardness	90A
Nozzle Temperature	220–240°C
Bed Temperature	40–60°C
Print Speed	25–40 mm/s
Retraction	Minimal (1–2 mm) or disabled
Extruder Type Required	Direct drive preferred; Bowden possible with extreme care
Elongation at Break	400–600%
Multimaterial Compatible	No — too soft for AMS/MMU feed paths
Leading Products	NinjaTek Edge (83A), select eSun and Fillamentum offerings

When to choose 90A over 95A: When the part needs genuine compressibility — a gasket that seals under light clamping force, a wearable that conforms to skin, or a grip that deforms under finger pressure. For most other applications, 95A with 20–40% infill produces comparable results with much easier printing.

03 — 95A TPU: The Industry Standard

95A is the default TPU grade — the one most manufacturers produce, most printers handle, and most users reach for first. It is flexible enough for phone cases, drone bumpers, wheels, straps, and feet, but firm enough to feed through any direct-drive extruder and most Bowden setups. Think of it as the skateboard wheel of 3D printing.

Property	Value
Shore Hardness	95A
Nozzle Temperature	220–240°C
Bed Temperature	40–60°C
Print Speed	40–60 mm/s (up to 200 mm/s on high-flow variants)
Retraction	1–3 mm at 25 mm/s
Extruder Type Required	Direct drive or Bowden (with care at 25–30 mm/s)
Elongation at Break	400–650%
Multimaterial Compatible	No for standard 95A — external spool only. Bambu TPU for AMS (68D) is the AMS-compatible exception.
Leading Products	Polymaker PolyFlex TPU95, Overture TPU, eSun TPU 95A, NinjaTek Cheetah (95A), SainSmart TPU

High-speed TPU 95A: A new class of formulations (Polymaker PolyFlex TPU95-HF, iSANMATE HS TPU 95A, Bambu TPU 95A HF) optimized for faster melt flow. These materials print at 150–200 mm/s on compatible printers — triple the speed of standard 95A — without sacrificing elasticity or layer adhesion. The high-flow formulation reduces the viscosity bottleneck that normally limits TPU print speed.

04 — 98A TPU: Semi-Rigid Flexibility

98A is the firmest end of the Shore A scale for FDM printing. Thin walls at 98A feel almost rigid — the flex is there under deliberate force but doesn't happen under light handling. Think of it as hard rubber: impact-resistant, durable, and abrasion-resistant, with just enough give to absorb shock.

Property	Value
Shore Hardness	98A
Nozzle Temperature	225–245°C
Bed Temperature	50–60°C
Print Speed	30–50 mm/s
Retraction	1–3 mm
Extruder Type Required	Any — direct drive or Bowden
Elongation at Break	80–100%
Multimaterial Compatible	Yes — runs on AMS and MMU with care
Leading Products	NinjaTek Armadillo (75D), MatterHackers PRO Series Flex

When to choose 98A: When you need impact resistance and abrasion resistance without the part feeling rubbery. Housings, enclosures, bumpers, wheels, and structural components that must absorb drops without cracking. 98A prints like PETG with slightly more patience and produces parts that are nearly as stiff as rigid plastics but can survive impacts that would shatter PLA.

05 — 60D–68D: Semi-Rigid AMS-Compatible TPU

Shore D grades of TPU are stiff enough to feel like hard plastic with a slight give. They exist primarily to fill a specific gap: multimaterial system compatibility. Bambu Lab's TPU for AMS at 68D is the flagship product in this category — the only TPU that can reliably feed through the Bambu AMS and AMS Lite automatic material systems.

Property	Bambu TPU for AMS (68D)
Shore Hardness	68D
Nozzle Temperature	220–240°C
Bed Temperature	30–35°C (with glue)
Print Speed	Up to 250 mm/s (60% faster than TPU 95A HF)
Max Volumetric Speed	18 mm³/s
Elongation at Break	> 650%
AMS / AMS Lite Compatible	Yes — all AMS series
Nozzle Compatibility	0.4mm, 0.6mm, 0.8mm hardened steel. 0.2mm NOT compatible.
Limitation	68D is firmer than 98A — impact-resistant but not "rubbery"

The AMS trade-off: Bambu's TPU for AMS is a remarkable engineering achievement — it solves the problem that has frustrated every Bambu printer owner who wanted multicolor flexible prints. But the 68D hardness is a deliberate compromise: the filament must be stiff enough to survive the AMS's long PTFE path and sharp drive engagements without buckling. If your application genuinely needs rubbery flex (85A–95A), you must print from the external spool holder — which the direct-drive toolhead handles perfectly. If your application needs impact resistance and multi-material printing, 68D AMS TPU is the answer.

Multimaterial Printer Compatibility: What Actually Works

The biggest misconception in flexible 3D printing is that "TPU" is a single material you can load into any printer. In reality, each shore hardness grade has different hardware requirements, and the constraints become dramatically tighter when multimaterial systems are involved.

Why Soft TPU Cannot Run Through AMS / MMU Systems

Automatic Material Systems — Bambu AMS, Prusa MMU, Creality CFS — all share the same fundamental architecture: filament is pushed through long PTFE tubes with multiple drive gear engagements and sharp path changes. This design works perfectly for rigid filaments (PLA, PETG, ABS) because they maintain columnar strength when pushed. Soft TPU (95A and below) compresses inside the PTFE tube, buckles at the drive gears, and jams the system. The softer the filament, the worse this problem becomes.

Printer Compatibility Matrix by Shore Hardness

Printer Category	60A	75A	85A	90A	95A	98A	68D (AMS)
Bambu Lab (direct drive, external spool)	Possible	Yes	Yes	Yes	Yes	Yes	Yes
Bambu Lab (via AMS)	No	No	No	No	No	No	Yes
Prusa MK4/S+MMU3	No	No	No	No	Marginal	Possible	Possible
Direct drive (Ender 3 DD, Voron, etc.)	Possible	Yes	Yes	Yes	Yes	Yes	Yes
Bowden (Ender 3 stock, etc.)	No	No	No	Marginal	Yes (25–30 mm/s)	Yes	Yes
Dual nozzle (IDEX, H2D)	Possible	Yes	Yes	Yes	Yes	Yes	Yes

Key insight for ALT customers: If your project requires multimaterial printing with flexible materials, there are two viable paths. First, use Bambu TPU for AMS (68D) for multi-color or multi-material flexible parts through the AMS — but accept that the material will be semi-rigid rather than rubbery. Second, print the flexible component separately on a direct-drive setup and assemble it with rigid components after printing. ALT can evaluate your design and recommend the best approach.

Flexible Material Types Beyond TPU

TPU is the most common flexible filament, but it is not the only option. Each material type offers distinct properties that may better suit specific applications:

TPU (Thermoplastic Polyurethane)

The workhorse of flexible 3D printing. TPU offers excellent abrasion resistance, chemical resistance, and durability. It balances flexibility and strength better than any other flexible filament type. Available in the widest range of shore hardnesses (85A–98A) and the most manufacturer options. TPU is the default recommendation for most flexible applications.

TPE (Thermoplastic Elastomer)

A broader category that includes materials with rubber-like feel and higher elasticity than standard TPU. TPE is typically softer at equivalent hardness ratings and offers better grip. However, it is more challenging to print — requiring slower speeds and more precise extruder control. Best for applications where surface feel and grip are paramount: soft-touch grips, seals, and wearable contact surfaces.

TPC (Thermoplastic Copolyester)

An engineering-grade flexible material with excellent chemical resistance and thermal stability. TPC is less flexible than TPU but offers superior durability in harsh environments. It maintains flexibility at lower temperatures and resists oils, fuels, and solvents better than TPU. Best for automotive components, outdoor seals, and chemical-resistant gaskets.

Soft PLA

A modified PLA that offers rubber-like flexibility while retaining PLA's ease of printing. With a shore hardness typically around 92A, soft PLA prints at PLA temperatures and speeds, making it accessible to printers that cannot handle true TPU. It is biodegradable, which may be a requirement for certain applications. The trade-off: lower elongation and abrasion resistance than TPU.

TPA (Thermoplastic Polyamide)

A chemical co-polymer that blends TPE flexibility with nylon smoothness. TPA offers high flexibility, excellent surface finish, and durability against repeated bending. It bridges the gap between flexible elastomers and engineering nylons, making it suitable for functional prototypes that must flex without degrading over thousands of cycles.

PEBA (Polyether Block Amide)

A premium elastomer used in high-performance footwear and athletic equipment. PEBA offers extremely high rebound energy (spring-back), low density (lighter than TPU), and maintains flexibility across a wide temperature range. It is more expensive and harder to print than TPU, but delivers performance that TPU cannot match for applications requiring energy return: running shoe midsoles, impact-absorbing inserts, and sports protection.

Flexible Material Comparison

Property	TPU	TPE	TPC	Soft PLA	TPA	PEBA
Shore Hardness Range	85A–98A, 60D–68D	60A–90A	85A–95A	~92A	85A–95A	~95A
Print Difficulty	Easy (95A) to Hard (85A)	Moderate to Hard	Moderate	Easy — PLA-like	Moderate	Hard
Abrasion Resistance	Excellent	Good	Excellent	Fair	Very good	Good
Chemical Resistance	Good	Fair	Excellent	Fair	Good	Good
Temperature Resistance	Good (80–120°C)	Fair	Excellent (120°C+)	Low (~60°C)	Good	Excellent
Elongation at Break	400–700%	500–800%	300–500%	200–300%	400–600%	500%+
Biodegradable	No	No	No	Yes	No	No
Best For	General engineering, wearables, gaskets	Soft grips, seals, skin-contact	Automotive, chemical environments	Biodegradable flex, easy prototypes	Repeated flex cycles, smooth flex	Footwear, sports, energy return

Designing Parts for Flexible Materials

Flexible materials behave differently from rigid plastics during and after printing. These design principles improve both print success and final part performance:

01 — Control flexibility with wall loops and infill

The most powerful variable for controlling part flexibility is wall loop count. More walls = stiffer part. Fewer walls = more flexible. A phone case at 2 wall loops with 15% infill will flex easily; the same model at 5 wall loops with 60% infill will feel nearly rigid. Use this to tune the exact flexibility you need from a single material.

02 — Orient for layer adhesion strength

Flexible parts are weakest between layers. Design parts so that the primary flex direction is perpendicular to the layer lines — the part bends along the layers, not across them. A strap that bends around a wrist should be printed flat, not upright.

03 — Avoid thin walls and sharp corners

Thin walls (1–2 perimeters) in soft TPU can tear during use. Use at least 3 perimeters for structural flexible parts. Sharp internal corners create stress concentrations that crack under repeated flexing. Add generous fillets to internal corners — even 1–2 mm radius dramatically improves fatigue life.

04 — Design for print orientation

Overhangs and bridges in soft TPU are extremely difficult to print cleanly. Orient the part so that overhanging features face upward or at angles below 45°. Support material removal on soft TPU is risky — the support can tear the part surface. Design parts to minimize or eliminate the need for supports.

05 — Tune compression with infill pattern

Different infill patterns produce different compression behaviors. Gyroid and cubic infill produce uniform compression in all directions. Gyroid is preferred for wearables and gaskets because it compresses evenly and recovers quickly. Rectilinear infill compresses more in one direction — useful for directional seals.

06 — Consider moisture absorption in design

Most flexible filaments are hygroscopic — they absorb moisture from the air, which causes stringing, bubbling, and weak layer adhesion during printing. Dry all flexible filament before printing (70–80°C for 8–12 hours). For end-use parts exposed to humidity, TPU absorbs more moisture than PLA or PETG — account for dimensional changes in precision applications.

Flexible Materials in Practice

Prosthetic Liners and Wearable Interfaces

Medical-grade prosthetic liners require ultra-soft materials (75A–85A) that conform to skin, distribute pressure evenly, and withstand repeated donning and doffing. TPU and TPE in the 75A–85A range produce liners that are comfortable for all-day wear while maintaining structural integrity over thousands of use cycles.

Automotive Gaskets and Seals

Engine bay gaskets, weatherstripping, and fluid seals require chemical resistance, temperature stability, and compression set resistance. TPC and high-grade TPU (95A–98A) produce gaskets that resist oil, fuel, and coolant while maintaining seal pressure over thermal cycling. 3D-printed gaskets are commonly used for prototyping and low-volume production before committing to injection mold tooling.

Soft Robotics and Grippers

Soft robotic grippers use flexible materials to conform around objects without damaging them. NinjaFlex 85A and similar soft TPUs enable grippers that can handle fragile items — eggs, fruit, glass — with consistent pressure. Pneumatic soft actuators printed in 85A TPU inflate and deflate to create gripping motion.

Consumer Product Prototyping

Phone cases, watch bands, shoe soles, and ergonomic grips benefit from flexible materials that feel like the final injection-molded product. 95A TPU produces prototypes that closely match the feel and performance of mass-produced flexible consumer goods, enabling realistic user testing before production commitment.

Vibration Dampening and Mounts

Electronic enclosures, sensor housings, and motor mounts printed in 90A–95A TPU absorb vibration that would damage sensitive components or generate noise. TPU's inherent vibration-dampening properties make it ideal for mounting Raspberry Pi cases, drone flight controllers, and industrial sensor housings.

Flexible Materials Available at ALT

ALT stocks flexible filaments from leading manufacturers across multiple shore hardness grades. Our engineering team can recommend the optimal material and settings for your specific application:

Material	Hardness	Type	Print Speed	Best For	Supplier
NinjaFlex Chinchilla	75A	TPU	15–20 mm/s	Ultra-soft wearables, skin-contact	NinjaTek
NinjaFlex	85A	TPU	15–35 mm/s	Gaskets, seals, vibration dampening	NinjaTek
NinjaFlex Edge	83A	TPU	20–40 mm/s	Flexible with faster print speed	NinjaTek
NinjaTek Cheetah	95A	TPU	40–60 mm/s	General flexible parts, high-speed printing	NinjaTek
NinjaTek Armadillo	75D	TPU (semi-rigid)	30–50 mm/s	Impact-resistant, wear-resistant parts	NinjaTek
Polymaker PolyFlex TPU95	95A	TPU	40–60 mm/s	Dimensionally consistent general flex	Polymaker
Polymaker PolyFlex TPU95-HF	95A	TPU (high-flow)	Up to 200 mm/s	Rapid production, high-speed printers	Polymaker
Overture TPU	95A	TPU	40–60 mm/s	Budget-friendly entry TPU	Overture
Bambu TPU 95A HF	95A	TPU (high-flow)	Up to 147 mm/s	Bambu ecosystem, fast flexible	Bambu Lab
Bambu TPU for AMS	68D	TPU (AMS-compatible)	Up to 250 mm/s	Multi-color/multi-material flexible	Bambu Lab
SainSmart TPU	95A	TPU	30–50 mm/s	Forgiving entry-level flexible	SainSmart
eSun eTPU-95A	95A	TPU	40–60 mm/s	Reliable mid-range TPU	eSun
Fillamentum Flexfill	92A, 98A	TPU	30–50 mm/s	Food-contact applications, multiple hardnesses	Fillamentum

Need help selecting the right flexible material?

Every flexible application has unique requirements — shore hardness, chemical resistance, multimaterial compatibility, and print speed all influence material selection. ALT's additive manufacturing engineers evaluate your design and recommend the optimal flexible material, shore hardness, and print settings for your specific application. We ensure your flexible parts meet performance requirements on the first print.

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