Silicone Hardness Comparison Chart (Shore A): A Manufacturer's Guide

What Is Shore A Silicone Hardness?

• Compression and sealing behavior
• Flexibility and dimensional stability
• Grip, tactile feel, and surface contact
• Long-term durability under mechanical stress
• Sealing performance under pressure or temperature cycles

Silicone hardness refers to the resistance of silicone rubber to indentation. It is measured using the Shore A scale, the industry-standard method for elastomers used in sealing, instrumentation, and industrial applications. For a primer on silicone chemistry and composition, see our Silicone 101 overview

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Shore A Silicone Hardness Comparison Chart

Silicone rubber ranges from 0 Shore A (gel-like, ultra-soft) to 90 Shore A (near rigid). Selecting the wrong hardness is one of the most common and costly mistakes in silicone component specification. It leads to seal failure, deformation, or premature wear in service.

Our manufacturing sweet spot: We specialize in custom silicone from 30A to 60A, covering the full range of sealing and general-purpose instrumentation components.

How Shore A Hardness Is Measured

Shore A hardness is tested using a durometer, a standardized instrument that presses a flat-ended indenter into the silicone surface under a defined force. The depth of penetration determines the hardness value.

• 0A = full indenter penetration (completely soft)
• 100A = no penetration at all (completely rigid)

For instrumentation and industrial applications, hardness must be consistent across a production batch. Variation of even ±5 Shore A can affect sealing compression and flow control performance in precision components.

The Chemistry Behind Shore A: How Manufacturers Control Silicone Hardness

Silicone hardness does not come from the raw material alone. It is developed through a controlled production process, and understanding this helps explain why hardness consistency is a chemistry and process problem, not just a quality inspection problem. Learn what is silicone a comprehensive overview. 

The Supply Chain Behind a Shore A Value

Raw silicone gum is produced by chemical manufacturers, companies that synthesize the base polymer from silica (sand) and other compounds. As a custom silicone product manufacturer, we do not produce silicone gum. We work with it, selecting, compounding, and processing it to achieve a specific hardness and performance target for each application.

Each raw silicone gum arrives with a defined vinyl content, a chemical property that determines its hardening potential. For example, a gum with 0.04% vinyl content behaves differently under curing than one with 0.02%. The raw gum sets the ceiling. The formula we apply develops the actual hardness.

Vinyl Groups: The Hardening Mechanism

Vinyl groups are reactive sites along the silicone polymer chains, think of them as hooks. During vulcanization (curing under heat and pressure), a crosslinker bonds these hooks on adjacent chains together, forming a molecular network.

The density of that network determines Shore A hardness:

• More vinyl + more crosslinker = denser network = harder silicone (e.g. 70A–80A)
• Less vinyl + less crosslinker = looser network = softer silicone (e.g. 30A–40A)

Fillers, primarily silica, are also added to fine-tune hardness and improve mechanical properties like tear resistance. The final Shore A value is the result of the vinyl content, crosslinker ratio, filler loading, and cure conditions working together.

How We Hit a Target Hardness

We analyze the vinyl content of the incoming raw gum and calculate the compound formula needed to reach the target Shore A. This is verified by durometer measurement after a test cure before full production begins.

For intermediate hardness values, pre-compounded stocks can also be blended. For example, if a project requires 70A and we hold 60A and 80A stock, blending them in calculated proportions can achieve the target, which is useful during prototyping when speed matters.

This is why a reliable silicone manufacturer does not simply mold pre-mixed material and hope for the right result. Hardness is controlled at the compounding stage, before anything enters a mold.

Shore A Hardness Selection Guide by Application

Sealing Applications: 30A – 50A

For silicone seals, gaskets, O-rings, and diaphragms used in flow control, pressure sensing, and process instrumentation, the optimal range is 30A to 50A.

Why this range works:

• Soft enough to compress and conform to mating surfaces
• Firm enough to maintain sealing pressure across temperature cycles
• Resilient enough to recover shape after repeated compression

This is the range we produce most frequently for instrumentation clients requiring precision sealing in chemical, gas, and fluid measurement environments.

If silicone is too soft (below 20A), it deforms excessively under load and may extrude from the seal groove. If too hard (above 60A), it cannot compress sufficiently to form a reliable seal, especially on non-flat or machined metal surfaces.

General-Purpose and Keypads: 40A – 60A

For components where both flexibility and structural form are required, such as silicone keypads, protective covers, and cable management parts, 40A to 60A provides the right balance.

This range is common in:

• Industrial control panel keypads
• Silicone overmolded grips
• Instrument panel covers and protective boots

Mechanical and Structural Parts: 60A – 80A

For parts that must hold dimensional shape under sustained mechanical stress, such as structural housings, supports, or load-bearing components, harder silicone is preferred.

At 60A–80A, silicone provides:

• Better dimensional stability under compression load
• Higher resistance to surface wear
• Greater stiffness for structural integrity

Note: Silicone above 70A has reduced elasticity. For components exposed to repeated bending or compression cycling, this range may fatigue over time. Testing under real operating conditions is strongly recommended before finalizing.

Shore A Hardness: Application Reference Table

Shore A vs Compression Resistance

Hardness Behavior in Instrumentation Environments

Instrumentation silicone components operate in demanding conditions, including chemical exposure, wide temperature swings, and pressure cycling. Hardness selection must account for more than just static feel.

Temperature effects: Silicone becomes temporarily stiffer at low temperatures and slightly softer at elevated temperatures. For components used in process instrumentation across a wide temperature range, a 40A–50A baseline typically provides the most consistent sealing performance across operating conditions. Learn how silicone can handle high heat.

Chemical exposure: In aggressive chemical environments (acids, solvents, oils), silicone can swell slightly, effectively reducing functional hardness. Specifying a slightly harder baseline, for example 50A instead of 40A, can compensate for this in harsh media applications.

Compression set: Over time, silicone under sustained compression loses some recovery. Lower hardness silicone (below 30A) is more vulnerable to permanent compression set. For long-service-life seals in flow meters, pressure transmitters, or analyzers, 40A–60A provides better long-term recovery.

Shore A vs Shore 00: When Does Shore A Not Apply?

For extremely soft elastomers, softer than 10 Shore A, the Shore 00 scale is sometimes used. This is less common in industrial silicone but relevant for cushioning and ultra-soft gel applications.

For instrumentation and industrial silicone, Shore A is the relevant scale in virtually all standard applications.

How We Select Hardness for Custom Silicone Components

As a custom silicone manufacturer working with instrumentation OEMs and industrial clients, we typically follow this process when specifying hardness for a new component:

1. Understand the sealing environment: static or dynamic? What media? What pressure and temperature range?
2. Review mating surface geometry: harder surfaces (machined metal) generally require softer silicone to achieve consistent contact sealing.
3. Identify mechanical load requirements: parts under sustained compression need better compression set resistance.
4. Recommend a starting hardness: typically 40A or 50A for most sealing applications, adjusted based on the above factors.
5. Prototype and test: we strongly recommend testing at a minimum of two hardness levels before finalizing the production spec.

Common prototyping sets we supply: 30A, 40A, and 50A samples for direct comparison in the customer's actual assembly.

Prototyping Tip: Test Before You Finalize

Material hardness often behaves differently in a real assembly than expected from specification alone. A seal that appears correct on paper may be too hard to compress fully in a narrow groove, or too soft to hold position during installation.

Before committing to production volumes, we recommend:

• Testing at two adjacent hardness levels (e.g., 40A and 50A)
• Evaluating under actual compression load and media conditions
• Checking for compression set after a defined soak period

This step consistently reduces the risk of field failures and redesign costs, particularly for precision instrumentation seals where replacement is costly and downtime is not acceptable.

Video Demonstration

To see how different Shore A hardness levels actually behave, including compression, bending, and surface contact, watch this side-by-side comparison using real silicone samples:

Seeing the physical difference between 30A, 50A, and 70A silicone makes the selection decision significantly clearer than specification sheets alone.

Need a Custom Shore A Specification?

We manufacture custom silicone components across the 30A to 60A range for instrumentation OEMs, industrial equipment manufacturers, and product companies requiring precision-spec silicone rubber parts.

If you have a sealing, diaphragm, gasket, or molded silicone requirement and need guidance on hardness selection, contact our engineering team with your application details.

Frequently Asked Questions: Shore A Silicone Hardness