Selecting the wrong silicone hardness can result in inadequate sealing, insufficient durability, or improper fit when assembling precision components. Understanding the Shore hardness of silicone will help you to make decisions for your project with confidence. If you are unsure which hardness to select for your silicone project, this article serves as a guide to help you make the right choice.
What Is The Shore Hardness in Silicone Rubber
Shore Hardness is a standard used to measure a material’s resistance, primarily for elastomers such as rubber, plastics, and silicone. We measure Shore hardness by indenting the material with a hardness tester— the deeper the indentation, the lower the reading and the softer the material; conversely, the shallower the indentation, the higher the reading and the harder the material.
We usually divide Shore hardness into several scales, including Shore OO, Shore A, and Shore D.
The Shore OO scale is typically used for extremely soft materials—such as gel-like substances—including silicone pads, anatomical tissue models, and marshmallows.
The Shore A scale is generally applied to soft elastomers, such as rubber bands, silicone phone cases, and automobile tires.
The Shore D scale is typically used for hard plastics and semi-rigid rubbers, such as construction hard hats, bowling balls, and rigid piping.
And the silicone products we will be examining in depth in this article typically possess a Shore hardness ranging from 10A to 80A.
How Hardness Impacts Silicone Rubber Performance
Shore hardness determines the physical properties of silicone, so different silicone hardness results in distinct performance characteristics regarding a product’s sealing capability, durability, texture, and resilience.
Sealing Efficiency
Silicone in the low-hardness range (10A–30A) possesses exceptional conformability. This high conformability means that the silicone’s shape can be freely altered to suit your specific requirements.
Low-hardness silicone can easily fill scratches or irregularities in surfaces resulting from rough machining; by extruding into minute crevices, this low-hardness silicone will level out the product’s surface. Consequently, it serves as an important material for connecting components that are sensitive to pressure.
Within the medium-hardness range (40A–60A), this material strikes a balance between free deformation and high resilience. Its exceptional rebound ensures that even after prolonged compression, it retains sufficient outward tension to achieve the long-term sealing performance required by customers.
Silicone in the high-hardness range (70A–90A) is capable of withstanding high pressure. In environments involving high-pressure hydraulics or gases, high-hardness silicone does not easily deform or shear. Its exceptionally high extrusion resistance ensures that it maintains its shape under high pressure, preventing it from being forced into crevices and thereby causing seal failure.
Durability
In terms of durability, silicone within the medium-hardness range (40A–60A) exhibits excellent toughness, resisting breakage when subjected to stretching or twisting. It offers a high installation tolerance, which accommodates situations involving excessive force during installation or hardness tolerances in the parts. Silicone in this range is widely utilized in products that require frequent stretching and twisting.
High-hardness silicone exhibits superior wear resistance. It is capable of withstanding frequent sliding, and in the case of silicone with a hardness of 70A or higher, it can significantly extend the silicone lifespan.
Texture
The 10A–40A hardness range is primarily utilized to create skin-like textures, which are capable of simulating the human skin while eliminating the inherent stickiness of silicone. The 10A–20A sub-range is frequently employed in medical silicone wearables and stress-relief products—applications that specifically demand a realistic, body-like feel; conversely, the 30A–40A sub-range offers enhanced resilience and is a preferred choice for the infant products.
Silicone within the 50A–60A hardness range strikes a balance between molding precision and tactile feedback. When you use it for buttons, this type of silicone prevents users from perceiving a mushy or unresponsive feel. Furthermore, when utilized as watch straps for smart wearables or similar devices, it conforms perfectly to the natural contours of the wrist.
With a hardness range of 70A–85A, it typically offers a tactile sensation of strength and stability. Its high friction and wear-resistant properties make it widely used in industrial grips and the housings of outdoor equipment. If your product requirements fall into this category, this hardness range is the ideal choice for you.
Rebound
Silicone in the low-hardness range (10A–30A) exhibits a slow and gentle rebound response, which means it is capable of absorbing the majority of impact vibrations—a characteristic that makes it highly suitable for products requiring shock absorption and noise dampening.
The medium-hardness range (30A–60A) strikes the optimal balance regarding silicone’s rebound. When you apply pressure to it, it can generate a strong rebound force after compression feedback, thus returning to its original shape. The key advantage of silicone within this hardness range is its ability to withstand tens of thousands of repeated compression cycles without easily losing its elastic resilience.
Consequently, silicone in this hardness range serves as the ideal material choice for customers requiring silicone buttons and domes.
Silicone in the high-hardness range exhibits a rebound response that is swift and forceful. It is frequently selected by customers requiring high-pressure sealing rings.
If your priority lies not in the speed of the rebound but rather in its forcefulness, then high-hardness silicone is the best choice for you.
How to Use Shore Hardness in Applications
10A – 20A
Silicone within this range possesses a soft tactile quality; resembling a gel, it mimics the feel of human muscle or tissue. This hardness level is engineered to achieve a high degree of deformation under low pressure.
Silicone in the low Shore hardness range is capable of conforming to any shape, allowing it to fill even the most minute gaps or depressions and exerting minimal counter-force against the devices to which it is bonded.
The housings of many electronic products are constructed from thin plastic or brittle materials. Gel-like silicone acts as a buffer between the screws and the plastic casing. As you tighten the screws, the soft silicone evenly distributes the pressure, thereby preventing damage to delicate components.
Furthermore, due to its tactile resemblance to human tissue, soft silicone within this hardness range is widely utilized in wearable medical devices.
Soft silicone possesses a high damping effect, enabling it to absorb shockwaves and vibrations upon impact to achieve effective shock absorption and cushioning. You can utilize it to provide vibration damping for hard disk drives or to prevent instability in optical equipment.
30A – 50A
A Shore hardness range of 30A to 50A represents the “golden zone” for silicone hardness. Medium-hardness silicone possesses exceptional elastic memory, allowing its stretch and tear resistance to reach its maximum, while also demonstrating outstanding resilience.
When used in infant products—such as pacifiers and teething toys—it exhibits exceptional resilience, rarely undergoing fatigue deformation even after repeated compression.
It is also suitable for use in electronic accessories, such as silicone keyboards and mobile phone cases. Its medium-range hardness provides excellent tactile feedback while effectively protecting the device.
Furthermore, it is widely utilized in applications requiring waterproofing—such as water bottle stoppers and sealing components for appliance fluid systems—to ensure effective water resistance.
60A – 80A
Silicone within this range of Shore hardness possesses a tactile feel similar to that of a car tire or rigid leather. Its primary advantages lie in the material’s inherent durability and resilience.
In contrast to soft silicones, high-hardness silicone exhibits exceptional resistance to extrusion. In industrial applications, this material is utilized in components such as conveyor belts and rollers, where it serves a dual function: providing a cushioning effect while preventing the material from being squeezed into equipment gaps—a scenario that could otherwise lead to mechanical failure.
Its high load-bearing capacity allows it to serve as structural support when applied to heavy-industry sealing components—such as high-pressure hydraulic seals, petrochemical pipeline gaskets, and high-temperature, high-pressure valve seals.
You can also utilize it to provide professional-grade protection for hand tools, as its high abrasion resistance translates to high frictional force, making it suitable for use as non-slip handles for power tools such as electric drills and saws.
Manufacturing Considerations & Tips
Process Selection Based on Hardness
Materials of varying hardness require correspondingly matched processing techniques.
When you specify extremely soft silicone with a hardness of less than 20A, its inherent softness makes it highly susceptible to tearing during the demolding stage of the manufacturing process. Conversely, if you select extremely hard silicones such as 70A as the raw material for your project, its excessive hardness may prevent it from flowing properly within the mold, often resulting in products with incomplete corners or edges.
In this regard, if your specific requirement is to customize silicone materials of such extreme hardness, we must adopt distinct silicone manufacturing processes.
For soft silicone, we utilize the LSR process, employing injection molding techniques to minimize tearing. Conversely, for hard silicone, we widen the runners and increase the air vents to ensure the silicone compound fills the mold.
Managing Hardness Tolerances for Precision
Silicone is a flexible material. it unlike a block of steel, it cannot achieve absolute precision in hardness. As it is inevitably influenced by environmental factors, material formulations, and manufacturing processes, tolerances will naturally occur; industry-standard tolerances typically fall within a range of ±5 Shore A.
If you require stricter tolerance control, we do have several countermeasures available.
The production of silicone typically requires a post-curing process. However, this step will cause the material’s hardness to increase by 1–2 degrees. To account for this outcome, factories typically apply a formula pre-adjustment, which lowers the target hardness of the raw material mixture. This ensures that the final hardness achieved after curing is precisely as intended.
Since raw materials from different batches may exhibit subtle variations—and because you require the thousandth silicone product to be absolutely identical to the first—we typically utilize a single, dedicated batch of raw materials for production. Furthermore, we provide a “first-off” sample for your approval and benchmarking before proceeding with mass production.
Certain precision parts can be rendered defective by fluctuations of just 5 Shore A. However, utilizing the LSR process allows mold temperature fluctuations to be controlled within 1°C, thereby facilitating more precise control over the hardness of the finished product.
Managing Environmental Effects on Material Hardness
The hardness of silicone is susceptible to environmental factors; in other words, the initial hardness does not necessarily represent the final hardness. Therefore, we take these environmental variables into account during the design phase.
Excessive heat causes silicone to vulcanize prematurely, while excessive cold leads to reduced flowability. To address this, we store the silicone material in a temperature- and humidity-controlled warehouse; this controlled indoor environment ensures that the material remains in a consistent state when entering the mold.
Additionally, you can request that the production team establish a dynamic process database. This system is capable of making adjustments to temperature and timing based on the season and humidity levels, thereby ensuring consistent product hardness.
Do not forget to request that the factory implement a standardized cooling process: specifically, that—while the silicone products are still unformed immediately after demolding—the finished items be arranged evenly on specialized cooling racks to undergo natural cooling within a controlled environment, thereby ensuring highly consistent hardness.
FAQ
What Should I Do if My Project Requires Extremely Precise if the Industry-Standard Tolerance of ±5 Degrees Is Unacceptable for My Application?
For your precision components, we offer customized solutions designed to ensure strict control over product tolerances—a critical requirement for your project. Specifically, we implement a fully automated LSR (Liquid Silicone Rubber) manufacturing process and lock the raw materials to a single batch. While this approach may result in a slight fluctuation in unit cost, it ultimately yields substantial overall cost savings by significantly reducing scrap rates during assembly and minimizing after-sales service expenses.
Is Post-Curing a Mandatory Step? To What Extent Does It Influence the Final Stabilization of Hardness?
For sealing components and products specifically designed for infants, post-curing is important. It facilitates the volatilization of harmful substances and enhances the stability of the molecular structure. Typically, following this curing process, the product’s hardness increases by approximately 1 to 2 points. During the mold development and prototyping stages, we proactively incorporate this increment into our calculations and considerations. If you have extremely stringent requirements for dimensions and hardness, you’d better confirm whether post-curing is required before prototyping to prevent hardness deviations during mass production.
Should I Choose LSR or HCR? Is There a Difference in Hardness?
The hardness ranges of these two types of silicone rubber largely overlap. If you require small-batch production of large-scale products, we recommend using HCR, as it offers relatively lower costs. However, if your products are extremely small in size, demand exceptionally high precision, and require mass production, then the liquid silicone rubber properties would be superior. Since liquid silicone rubber is conveyed through a fully enclosed piping system, its hardness tolerance can be controlled within an extremely precise range, and the product surfaces remain free from secondary contamination.
Final Thoughts
Shore hardness is a critical factor influencing the performance and application of silicone products. If you have any concerns about selecting the Shore hardness for your silicone project, please contact us directly. As a silicone product manufacturer with over 20 years of experience, Legensilico offers comprehensive, one-stop silicone solutions to help you identify the option that best meets your requirements.
