Views: 0 Author: Kevin Fang Publish Time: 2026-06-09 Origin: Chensheng Medical
Table of Contents
If you have ever reviewed a silicone tubing datasheet or submitted a custom OEM inquiry, you have encountered the term Shore A hardness — typically expressed as a number between 20 and 80, followed by the letter "A." It appears on every technical data sheet, every material certificate, and nearly every product drawing for silicone components.
Yet it is one of the most commonly misunderstood and incorrectly specified parameters in medical silicone procurement. Engineers routinely specify Shore A values that are either too soft for the application (causing kinking, collapse, or dimensional instability) or unnecessarily firm (reducing patient comfort, increasing pump wear, or making assembly difficult).
This guide gives you a complete, practical understanding of Shore A hardness — what it measures, how it is tested, how it interacts with other design parameters, and how to select the right value for every major medical silicone application.
Shore A hardness is a standardized measure of a material's resistance to permanent indentation by a defined probe under a defined load. It is one of several Shore hardness scales developed by Albert Ferdinand Shore in the 1920s, each designed for different material stiffness ranges.
For silicone rubber — and elastomers in general — the Shore A scale is the standard measurement tool. The test is defined by ASTM D2240 (Standard Test Method for Rubber Property — Durometer Hardness) and its international equivalent ISO 48-4.
A Shore A durometer consists of a truncated cone-shaped indenter with a flat tip (0.79mm diameter), loaded by a calibrated spring. The indenter is pressed perpendicularly into the flat surface of the test specimen under a total force of 822 grams (8.06 N). The depth of penetration after a defined contact time (typically 15 seconds for time-dependent readings) is converted to a hardness value on a scale of 0 to 100:
0 = the indenter penetrates to its full depth (infinitely soft material)
100 = zero penetration (infinitely hard material — equivalent to steel)
In practice, medical silicone tubing and molded components span the range from approximately Shore A 10 (very soft, gel-like) to Shore A 80 (firm, stiff rubber).
For a valid Shore A measurement per ASTM D2240:
Minimum specimen thickness: 6.4mm (0.25 inches)
Flat, parallel surfaces required
Temperature: 23°C ± 2°C (results are temperature-dependent)
Minimum distance from edge: 12mm
Critical note for tubing: Shore A hardness is measured on flat slab specimens of the compound — not on the tube itself. A thin-wall tube cannot be directly measured with a durometer. The value on a tubing datasheet refers to the compound used to make the tube, tested on a flat slab. This is why wall thickness and Shore A hardness must always be considered together when evaluating tubing flexibility.
The Shore system includes multiple scales for different material types. Understanding which scale applies to your material prevents specification errors:
Scale | Indenter Type | Load | Applicable Materials | Typical Range |
Shore OO | Sphere (1.19mm radius) | 113g | Ultra-soft gels, foams, very soft elastomers | Silicone gels: 5–30 OO |
Shore A | Truncated cone (flat tip) | 822g | Soft to medium rubbers, elastomers, silicone | Medical silicone: 10–80 A |
Shore D | Sharp cone (30° tip) | 4,536g | Hard rubbers, rigid plastics, hard elastomers | Hard silicone: 80+ A / 20–80 D |
For medical silicone tubing and molded components, Shore A is always the correct scale. Shore D is used for hard thermoplastics (ABS, PC, nylon) used in device housings and rigid components — not for silicone.
The scales overlap at the extremes: a material measuring Shore A 90–100 can also be measured on the Shore D scale. A material measuring Shore A 10–20 may be better characterized on the Shore OO scale for precision. For the vast majority of medical silicone applications (Shore A 20–80), the Shore A scale provides clear, unambiguous measurements.
Medical silicone is available across a wide hardness range. Here is what each range feels like and where it is used:
Physical feel: Barely perceptible resistance to touch; deforms under the weight of a finger; recovers slowly.
Material behavior:
Extremely high elongation (600–800%)
Very low tear resistance — handle with care
Excellent conformability to irregular surfaces
Prone to dimensional instability under any load
Medical applications:
Neonatal skin-contact components (pressure relief)
Soft tissue simulation and training models
Implant-adjacent cushioning components
Specialty wound contact interfaces
Not suitable for: Any application requiring dimensional stability, fluid containment under pressure, or pump contact.
Physical feel: Noticeably soft; easily deformed with light finger pressure; quick elastic recovery.
Material behavior:
High elongation (500–700%)
Moderate tear resistance
Excellent flexibility — resists kinking at very small bend radii
Low compression set resistance — not suitable for dynamic compression
Medical applications:
Neonatal and pediatric feeding tubes (patient comfort priority)
Soft drainage tubes for sensitive anatomical locations
Gentle patient-contact tubing (nasal, oral)
Balloon components requiring high compliance
Specialty catheter tips for atraumatic insertion
Chensheng Medical note: Our neonatal feeding tube range uses Shore A 25–30 platinum-cured compound to achieve the combination of softness and dimensional precision required for NICU applications. Learn more about our medical silicone tubing product range.
Physical feel: Soft and pliable; deforms easily under moderate finger pressure; springs back quickly.
Material behavior:
Good elongation (400–600%)
Good tear resistance
Excellent flexibility for general fluid transfer
Adequate compression set for low-frequency dynamic applications
Medical applications:
General-purpose IV fluid transfer tubing
Standard urological drainage tubing
Enteral feeding tubes (adult)
Nasogastric tube bodies
Soft catheter shafts
General medical fluid handling tubing
This is the most widely used hardness range for standard medical tubing. It represents the best balance of flexibility, dimensional stability, and ease of assembly for the majority of fluid transfer applications.
Physical feel: Noticeably firmer; requires deliberate force to deform; snaps back immediately upon release.
Material behavior:
Good elongation (350–500%)
High tear resistance
Excellent compression set resistance (≤8% at 22h/70°C)
Optimal fatigue resistance under cyclic compression
Good dimensional stability under pressure
Medical applications:
Peristaltic pump tubing (the primary application for this range)
Respiratory circuit tubing (adult ventilator circuits)
Anesthesia breathing circuit components
High-flow fluid transfer tubing
Pump segments for infusion pumps
Tubing requiring resistance to external compression
Why Shore A 50–65 is critical for peristaltic pump tubing: Peristaltic pumps work by repeatedly compressing and releasing the tubing. The tubing must recover its full circular cross-section between roller contacts to maintain accurate flow rates. Too soft (below Shore A 45) and the tube recovers slowly, causing flow rate drift and eventual collapse. Too firm (above Shore A 70) and the pump motor must work harder, increasing wear on both the tube and the pump head. Shore A 55–62 is the optimal range for most peristaltic pump applications.
For a complete technical guide to peristaltic pump tubing selection — including compression set testing, fatigue life, and pump head compatibility — see: Peristaltic Pump Tubing Selection: Material Properties and Performance Factors
Physical feel: Distinctly firm; requires significant force to deform; minimal visible deflection under hand pressure.
Material behavior:
Moderate elongation (200–400%)
Very high tear resistance
Excellent pressure rating
High dimensional stability
Reduced flexibility — minimum bend radius increases significantly
Medical applications:
High-pressure fluid transfer tubing
Structural silicone components in device assemblies
Silicone gaskets and seals requiring high compression resistance
Connector bodies and rigid interface components
Tubing requiring resistance to internal pressure (>3 bar)
Silicone O-rings for static sealing applications
Caution: At Shore A 70+, silicone tubing becomes noticeably stiff. For patient-contact or flexible fluid transfer applications, this range is rarely appropriate. Verify that the stiffness is genuinely required before specifying above Shore A 65.
This is the most important concept in silicone tubing specification — and the most frequently overlooked.
Shore A hardness measures the material. Wall thickness determines how that material behaves as a tube.
Two tubes can have identical Shore A hardness but completely different flexibility if their wall thicknesses differ. Conversely, two tubes can feel equally flexible despite having different Shore A values if their wall thicknesses are adjusted accordingly.
The bending stiffness of a tube scales approximately with the cube of wall thickness for thin-walled tubes:
Bending Stiffness∝E×t3Bending Stiffness∝E×t3
Where EE is the elastic modulus (directly related to Shore A hardness) and tt is wall thickness.
This means: doubling the wall thickness increases bending stiffness by approximately 8× — far more than the effect of changing Shore A hardness within the normal medical range.
Scenario | Shore A | Wall Thickness | Result |
Standard IV tubing | 45 | 1.0mm | Flexible, easy to handle |
Same compound, thicker wall | 45 | 2.5mm | Noticeably stiffer — may be too stiff for IV use |
Firmer compound, thin wall | 60 | 0.8mm | Similar flexibility to the first example |
Pump tubing | 60 | 1.6mm | Firm enough for compression recovery, flexible enough for routing |
High-pressure tubing | 70 | 3.0mm | Very stiff — intentional for pressure containment |
Design rule: When you need a tube that is both flexible (for routing and patient comfort) AND dimensionally stable (for accurate flow rates or pressure containment), the solution is often a thinner wall in a slightly firmer compound — not a softer compound with a thicker wall. Discuss this trade-off with your supplier's applications engineering team before finalizing your specification.
When you change Shore A hardness, you change multiple mechanical properties simultaneously. Here is how the key properties shift across the medical silicone hardness range:
Property | Shore A 20–30 | Shore A 40–50 | Shore A 55–65 | Shore A 70–80 |
Tensile strength (MPa) | 4–6 | 7–9 | 8–11 | 9–12 |
Elongation at break (%) | 600–800 | 400–600 | 350–500 | 200–400 |
Tear resistance (kN/m) | 10–18 | 20–28 | 25–35 | 30–40 |
Compression set (%, 22h/70°C) | 15–25 | 10–18 | 6–12 | 5–10 |
Flexibility | Excellent | Very good | Good | Moderate |
Kink resistance | Low | Moderate | Good | Very good |
Pressure rating | Very low | Low–moderate | Moderate | High |
Pump suitability | Poor | Marginal | Excellent | Poor (too stiff) |
Patient comfort | Excellent | Very good | Good | Poor |
Values are typical ranges for platinum-cured medical silicone. Actual values depend on specific compound formulation.
Compression set is the percentage of deformation that remains after a compression load is removed. A compression set of 10% means the tube does not fully recover 10% of its original diameter after being compressed.
For peristaltic pump tubing, compression set directly determines:
Flow rate accuracy over time — as compression set accumulates, the effective ID decreases, reducing flow rate
Tube service life — high compression set leads to permanent deformation and eventual tube collapse
Pump calibration stability — pumps calibrated at installation drift as compression set increases
This is why platinum-cured silicone is non-negotiable for pump tubing — its compression set values (6–10%) are significantly better than peroxide-cured silicone (15–25%). For a detailed comparison of curing chemistry and its effect on mechanical properties, see: Platinum-Cured vs. Peroxide-Cured Silicone: Which Is Better for Your Application?
Use this table as your starting point for Shore A specification. Always validate with functional testing in your specific application.
Application | Recommended Shore A | Wall Thickness Guidance | Key Rationale |
Neonatal feeding tube | 20–30 | 0.5–0.8mm | Patient comfort, atraumatic insertion |
Adult nasogastric (NG) tube | 30–40 | 0.8–1.2mm | Comfort + sufficient stiffness for placement |
PEG / gastrostomy tube | 40–55 | 1.0–1.5mm | Durability for long-term indwelling use |
IV fluid transfer tubing | 40–55 | 1.0–1.5mm | Flexibility, transparency, easy assembly |
Urological drainage tubing | 35–50 | 1.0–1.5mm | Patient comfort, kink resistance |
Wound drainage tubing | 40–55 | 1.2–2.0mm | Kink resistance, tissue compatibility |
Peristaltic pump segment | 55–65 | 1.2–2.0mm | Compression set, fatigue life, flow accuracy |
Infusion pump segment | 55–62 | 1.4–1.8mm | Compression recovery, calibration stability |
Adult ventilator circuit | 55–65 | 1.5–2.5mm | Kink resistance, low compliance, durability |
Pediatric ventilator circuit | 55–65 | 1.2–2.0mm | Kink resistance, lower dead space |
Neonatal ventilator circuit | 60–70 | 1.0–1.5mm | Dimensional stability, minimal dead space |
Anesthesia breathing circuit | 55–65 | 1.5–2.5mm | Low compliance, kink resistance, durability |
High-pressure fluid transfer | 65–75 | 2.5–5.0mm | Pressure containment |
Silicone O-ring / gasket (static) | 60–70 | N/A (molded) | Sealing force, compression set |
Silicone O-ring / gasket (dynamic) | 50–60 | N/A (molded) | Wear resistance, sealing under motion |
Balloon catheter balloon | 20–35 | 0.3–0.6mm | High compliance, low inflation pressure |
Foley catheter shaft | 40–55 | 1.0–1.5mm | Comfort, kink resistance, durability |
Surgical drain (Penrose type) | 30–45 | 0.5–1.0mm | Tissue compatibility, flexibility |
Pharmaceutical fluid transfer | 45–60 | 1.0–2.0mm | Low extractables, dimensional stability |
Micro-bore analytical tubing | 50–65 | 0.3–0.8mm | Dimensional precision, chemical inertness |
For respiratory circuit applications, see our detailed compliance guide: Medical-Grade Silicone Tubing for Respiratory Circuits: Compliance Requirements
When placing a custom OEM order for medical silicone tubing or molded components, Shore A hardness should be specified as follows:
Specify a target value with an acceptable tolerance band:
Example: Shore A 60 ± 5
This allows the manufacturer to use a qualified compound within the acceptable range
Tolerance of ±5 Shore A units is standard; ±3 is achievable for precision applications
Specify an acceptable range:
Example: Shore A 55–65
Equivalent to Option 1 but expressed as a range
Useful when the application has a clear performance window
For critical applications, specify the performance requirement rather than the hardness:
Example: "Compression set ≤ 8% per ASTM D395 Method B, 22h at 70°C"
This allows the manufacturer to optimize the compound for the performance outcome
Requires incoming inspection testing to verify compliance
Best practice: For peristaltic pump tubing, always specify both Shore A hardness AND compression set — hardness alone does not guarantee pump performance. Two compounds at Shore A 60 can have very different compression set values depending on their formulation and curing system.
A complete silicone tubing drawing should specify:
Inner diameter (ID) with tolerance
Outer diameter (OD) with tolerance
Wall thickness (WT) with tolerance — note: only two of three are independent
Shore A hardness with tolerance
Color (transparent / specified color)
Curing system (platinum-cured — always for medical)
Applicable certifications (USP Class VI, ISO 10993, FDA 21 CFR 177.2600)
Special requirements (radiopaque stripe, cleanroom packaging, sterilization)
For guidance on the complete custom OEM development process — from drawing submission through tooling, sampling, and production approval — visit our medical silicone products page or contact our applications engineering team directly.
When receiving medical silicone tubing from any supplier, Shore A hardness should be verified as part of your incoming inspection protocol.
Because tubing cannot be directly measured with a standard durometer (insufficient thickness, curved surface), there are two approaches:
Approach 1: Request compound slab test specimensAsk your supplier to provide flat slab specimens (minimum 6.4mm thick) of the same compound batch used for your tubing. Measure per ASTM D2240 at 23°C ± 2°C.
Approach 2: Verify against lot-specific CoARequest a lot-specific Certificate of Analysis (CoA) that includes the actual Shore A measurement for the compound lot used in your production run. Verify the reported value is within your specified tolerance.
Approach 3: Micro-durometer for thin sectionsFor thin-wall tubing where slab specimens are not available, a micro-durometer (Shore M scale) can be used on the tube wall directly. Note that micro-durometer values are not directly equivalent to standard Shore A values — establish a correlation factor with your supplier.
CoA shows only nominal value, not actual measured value: The supplier may be copying the compound specification rather than testing each lot. Request actual test data.
Shore A value outside specification by more than 3 units: Indicates compound formulation inconsistency or wrong compound used. Initiate supplier CAPA.
Shore A correct but compression set high: Indicates peroxide-cured compound may have been substituted. Request curing system confirmation.
For guidance on evaluating supplier quality systems and documentation, see: How to Choose a Reliable Medical Silicone Manufacturer in China
Problem: Shore A alone does not define the flexibility of a tube. A Shore A 60 tube with 0.8mm wall is more flexible than a Shore A 40 tube with 3.0mm wall.Solution: Always specify Shore A and wall thickness together. If flexibility is the key requirement, specify the minimum bend radius instead.
Problem: You see a competitor's product listed as "Shore A 55" and specify the same value without understanding whether it is appropriate for your application.Solution: Use the application-to-hardness table above to verify the specification makes sense for your use case. If uncertain, request samples at Shore A 50, 55, and 60 and test functionally.
Problem: Shore A 40 feels soft and flexible — which seems desirable. But it has poor compression set recovery, leading to flow rate drift and premature tube failure in peristaltic pump applications.Solution: For peristaltic pump tubing, specify Shore A 55–65 regardless of how firm it feels. The compression set performance, not the feel, is what matters.
Problem: High Shore A was specified for "durability" or "pressure resistance" without considering that the resulting stiffness is uncomfortable for patients and may cause tissue trauma.Solution: For patient-contact applications, Shore A 35–55 is almost always sufficient. Use wall thickness and reinforcement (braid, spiral) to achieve pressure resistance rather than increasing hardness.
Problem: Shore A hardness decreases as temperature increases. A tube specified at Shore A 60 at 23°C may measure Shore A 50–55 at body temperature (37°C) and Shore A 40–45 at autoclave temperature (121°C).Solution: For applications where operating temperature differs significantly from 23°C, request hardness measurements at the actual operating temperature, or apply a correction factor.
Q1: What Shore A hardness should I specify for standard medical silicone tubing?
A: For general-purpose medical fluid transfer tubing (IV lines, drainage, general fluid handling), Shore A 40–55 is the standard starting point. This range provides the best combination of flexibility, dimensional stability, and ease of assembly for the majority of medical applications. If you have a specific application — pump tubing, respiratory circuits, neonatal use — refer to the application-to-hardness table above or contact our applications engineering team for a specific recommendation.
Q2: Is there a difference between Shore A hardness and durometer hardness?
A: "Durometer hardness" is the general term for hardness measured with a durometer instrument. "Shore A hardness" specifies both the instrument type (Shore durometer) and the scale (A scale). In practice, the terms are used interchangeably for elastomers. When someone says "durometer 60" without specifying the scale, they almost always mean Shore A 60 for silicone rubber applications.
Q3: Can I get silicone tubing in any Shore A value, or are there standard grades?
A: Silicone compounds are available in a wide range of Shore A values, but manufacturers typically stock standard grades (commonly Shore A 30, 40, 50, 60, 70). Custom hardness values between these grades are achievable but may require a minimum order quantity to justify compound preparation. At Chensheng Medical, we maintain stock compounds at Shore A 30, 40, 50, 55, 60, and 70 for our medical tubing range. Custom hardness values are available for OEM orders with sufficient volume.
Q4: How does Shore A hardness affect the pressure rating of silicone tubing?
A: Shore A hardness has a secondary effect on pressure rating — wall thickness is the primary determinant. However, firmer compounds (Shore A 65–80) do provide higher burst pressure for a given wall thickness because of their higher elastic modulus. For high-pressure applications (>3 bar), we recommend combining adequate wall thickness with Shore A 65–75. For a given pressure requirement, our engineering team can calculate the minimum wall thickness and recommend the appropriate hardness.
Q5: Does Shore A hardness change after sterilization?
A: For platinum-cured silicone, Shore A hardness is highly stable across all standard sterilization methods. Autoclave cycling (up to 200 cycles at 134°C) typically produces less than 3 Shore A units of change. Gamma irradiation at standard doses (25–50 kGy) may produce a slight hardening effect (2–5 Shore A units) due to additional crosslinking. Peroxide-cured silicone shows greater post-sterilization property changes — another reason platinum-cured compounds are preferred for medical applications.
Q6: We are qualifying a new silicone tubing supplier. How do we verify Shore A hardness compliance?
A: Request lot-specific CoA data showing actual measured Shore A values (not just nominal compound specification). For critical applications, request compound slab specimens from the same production lot and verify independently per ASTM D2240 at 23°C ± 2°C. Include Shore A verification in your incoming inspection protocol with defined acceptance criteria (e.g., nominal ± 5 Shore A units). For guidance on the full supplier qualification process, see our article on how to choose a reliable medical silicone manufacturer in China.
Q7: What is the Shore A hardness of Chensheng Medical's standard medical tubing grades?
A: Our standard medical silicone tubing is available in Shore A 30, 40, 50, 55, 60, and 70. Our most commonly specified grades for medical device applications are Shore A 50 (general fluid transfer, catheters, drainage) and Shore A 60 (peristaltic pump tubing, respiratory circuits). All grades use platinum-cured compound manufactured in our ISO Class 7 cleanroom under ISO 13485 quality management. Contact our team for samples of any grade for your qualification testing.
Identify your primary application — pump tubing, patient-contact, structural, fluid transfer, or respiratory
Determine the dominant performance requirement — flexibility, compression set recovery, pressure rating, or patient comfort
Use the application-to-hardness table to identify the recommended Shore A range
Consider wall thickness together with Shore A — they interact to determine actual tube flexibility and stiffness
Request samples at two or three hardness values within the recommended range and validate functionally in your application before finalizing specification
When in doubt, our applications engineering team at Chensheng Medical is available to review your drawing, discuss your application requirements, and recommend the optimal Shore A specification — at no charge, as part of our standard pre-sales technical support.
Chensheng Medical manufactures platinum-cured medical silicone tubing across the full Shore A range (20–80) in our ISO 13485-certified, ISO Class 7 cleanroom facility. All products are supported by full biocompatibility documentation (USP Class VI, ISO 10993, FDA 21 CFR 177.2600) and lot-specific Certificates of Analysis.
→ Contact Our Applications Engineering Team→ Browse Our Medical Silicone Tubing Range→ Request Free Samples for Qualification Testing
Related Articles:
Platinum-Cured vs. Peroxide-Cured Silicone: Which Is Better for Your Application?
Peristaltic Pump Tubing Selection: Material Properties and Performance Factors
Medical-Grade Silicone Tubing for Respiratory Circuits: Compliance Requirements
How to Choose a Reliable Medical Silicone Manufacturer in China
