What determines whether a silicone product feels soft and stretchy or stiff and firm?
The answer lies in Shore hardness. It’s a standard way to measure how firm or soft silicone is. Whether you’re designing for comfort, flexibility, durability, or support, getting the right Shore hardness is key to performance and user satisfaction.
In this article, we’ll break down what silicone Shore hardness is, how it’s measured, the different scales like Shore 00, A, and D, and how to choose the right hardness for different applications. This guide will give you a clear and practical understanding of how Shore hardness impacts silicone products.
What Is Silicone Shore Hardness?
Shore hardness is a standard way to measure how hard or soft silicone is. If you want to know how firm a piece of silicone feels, we use a Shore durometer. This tool presses a pin into the surface with a set force and gives a reading from 0 to 100, based on how deep the pin goes.
In the silicone industry, we most commonly use the Shore 00, Shore A, or Shore D scales. A lower number means the silicone is softer and more flexible. A higher number means it’s harder and less elastic.
Shore hardness isn’t just a technical number. It affects how the product feels, performs, and fits its purpose. That’s why choosing and controlling the right hardness is so important when designing and making silicone products.
How Is Silicone Shore Hardness Classified?
Silicone has a wide range of hardness, from jelly-like softness to plastic-like rigidity. This can be adjusted by changing the formula. To measure it, we mainly use three standard scales: Shore 00, Shore A, and Shore D. Each scale runs from 0 to 100. The higher the number, the harder the silicone.
Shore 00: For Extremely Soft Materials
Shore 00 is specifically designed to measure extremely soft materials.
Typical Range: 10 to 90 Shore 00
Applications: Soft medical gels, pressure relief pads, special effects makeup
Shore A: The Most Commonly Used Scale
Shore A is the most common scale for silicone. It covers everything from soft rubber to semi-rigid parts.
Typical Range: 10 to 95 Shore A
Applications:
- Low Hardness (10A – 30A): Baby pacifiers, soft phone cases, medical tubes
- Medium Hardness (40A – 60A): Phone covers, kitchenware, O-rings
- High Hardness (70A – 90A): Silicone buttons, car seals, industrial gaskets
Shore D: For Hard Materials
For very hard silicone, we use the Shore D scale. It’s meant for hard rubber and plastics.
Typical Range: 20 to 90 Shore D
Applications: Hard seals, tool handles, industrial rollers
What Factors Affect the Shore Hardness of Silicone?
Shore hardness is an important properties of silicone. It influences how the product feels, how it performs, and whether it suits specific applications. But what exactly determines how soft or firm silicone is? Several factors, from chemical formulation to real-world usage, can make a big difference.
Raw Material Formulation
The chemical makeup of silicone is the foundation of its hardness. Even small changes in the base formula can lead to noticeable differences in the final product’s feel and performance.
- Siloxane backbone: The molecular weight and crosslink density directly affect hardness. A higher crosslink density increases hardness, but may reduce elasticity.
- Fillers: The type and amount of fillers like silica and calcium carbonate help adjust hardness. For example, increasing silica content can raise hardness to around 70 Shore A, but may reduce tear strength.
- Curing agents: Peroxide curing systems are often used for high-temperature vulcanized (HTV) silicone, suitable for harder products. Platinum catalysts are common in liquid silicone rubber (LSR), ideal for softer medical-grade items.
Manufacturing Process
Hardness isn’t only decided by what’s in silicone. How it’s processed during production also plays a key role.
- Curing conditions: High-temperature curing (150–200°C) increases crosslinking and raises hardness. Room-temperature vulcanization (RTV) is more suitable for softer products.
- Mixing process: Poor dispersion of fillers can cause uneven hardness and affect product quality.
- Post-curing: Secondary curing can fine-tune hardness and release residual stress.
Environmental and Use Conditions
Silicone doesn’t exist in a vacuum. Once in use, the environment and stress it faces can gradually change its hardness over time.
- Temperature: Silicone may soften under high heat and become slightly harder in cold temperatures. For instance, 20 Shore A silicone can feel like 25A at -40°C.
- Aging: Long-term exposure to UV light or chemicals may change hardness and shorten product life.
- Stress: Repeated compression or stretching may alter hardness, especially in softer silicones.
How Hardness Relates to Elasticity, Tensile Strength, and Tear Strength?
Silicone’s hardness, modulus of elasticity, tensile strength, and tear strength are all connected. These aren’t isolated traits. They reflect how tightly the silicone’s molecular network is cross-linked.
Modulus of Elasticity
This measures how much a material resists stretching and returns to its original shape.
Harder silicone usually has a higher modulus. It resists deformation more and feels stiffer.
That’s because harder silicone tends to have higher cross-link density, which limits chain movement and makes the material less flexible but more stable.
Tensile Strength
This is the max stress silicone can handle before snapping when pulled.
The link between hardness and tensile strength isn’t linear.
As hardness increases, tensile strength usually improves.
But too much hardness can backfire. The material becomes brittle and may snap more easily, since stress can’t spread evenly across overly stiff chains.
So, finding the right balance matters. A phone case, for example, needs enough hardness to protect, but also strength to avoid tearing or cracking.
Tear Strength
This shows how well silicone resists a crack from spreading once it starts.
For soft to medium silicones (20A–40A), adding some hardness usually boosts tear strength.
But if hardness climbs too high (above 60A–70A), tear strength may drop. The chains lose flexibility, so once a cut forms, it can tear quickly.
Tear strength is crucial for thin, edge-sensitive, or flexed items, like seals, gloves, or parts that get assembled and disassembled often.
What Happens If Silicone Is Too Hard or Too Soft?
What if silicone is too hard? What if it’s too soft? These are valid concerns. Extreme hardness values, in either direction, can seriously compromise a product’s performance and user experience.
There’s no one-size-fits-all answer. A phone case, a seal, or a keypad all require different balances. Too much hardness can ruin comfort or flexibility, while too little can lead to instability and wear.
To help clarify these risks, the table below outlines what problems may occur when silicone is either too hard or too soft, along with the potential trade-offs you’ll need to consider when making material choices.
| Hardness Condition | Potential Issues | Impact on Performance |
| Too Hard | Poor tactile feel and discomfort in user-facing products | Reduced comfort, especially for handheld or wearable items |
| Weak shock absorption | Less effective protection in drops or impact scenarios | |
| Inadequate sealing on irregular surfaces | Increased risk of leakage or air/fluid bypass | |
| Higher brittleness | Prone to cracking or breaking under stress or bending | |
| Difficult demolding | May tear or deform during manufacturing | |
| Poor low-temperature flexibility | May stiffen in cold environments, limiting function | |
| Too Soft | Lacks structural support | Easily deforms, loses shape stability |
| Poor abrasion and tear resistance | Wears out quickly, shorter product lifespan | |
| Slow rebound, poor keypress feel | Unsatisfactory tactile feedback for buttons or switches | |
| Hard to process during molding or post-processing | May not fill mold well, or too soft to handle after curing | |
| High compression set | Doesn’t recover after long-term compression, leading to function loss | |
| Surface attracts dust easily | Sticky texture may collect dust, reducing visual and hygienic appeal |
How to Choose the Right Silicone Hardness?
Picking the right silicone hardness isn’t random. It depends on how the product will be used, how it should feel, and how it needs to be made. Just like choosing shoe soles. Some need to cushion and others need to support.
Here’s a guide to picking the right hardness based on different uses.
Skin-Contact Products: Prioritizing “Skin-Friendly” Feel
For products that touch the skin, comfort and safety come first.
The recommended silicone hardness usually falls between 10A and 40A, sometimes even as soft as Shore 00.
Baby products like pacifiers, teethers, and nasal aspirators typically use silicone in the 20A to 30A range. This softness mimics the feel of skin and ensures safety and comfort for babies’ delicate mouths and skin.
Medical devices, such as catheters, respiratory masks, and prosthetic liners, have a broader hardness range from 10A to 50A depending on their function. For example, catheters often require a softness around 20A to provide flexibility, while prosthetic liners may need up to 50A to offer light support. Some ultra-soft scar patches even use Shore 00 silicone to achieve the maximum softness and conform closely to the skin.
Wearable devices like smartwatch straps and earphone tips generally fall between 30A and 50A. This range balances comfort and stability—too soft can feel loose, while too hard may cause discomfort.
Daily Consumer Goods & Kitchenware: Balancing Function and Feel
Daily consumer goods and kitchenware require silicone that is practical, durable, and comfortable to use.
The recommended hardness range for these products is generally between 40A and 70A.
Kitchenware items such as spatulas, baking molds, and lids usually use silicone from 40A to 60A. This range is tough enough to handle stirring and cooking tasks, while still flexible enough for easy use. Molds also need to release food easily and maintain their shape well.
Device protectors, including phone and tablet cases or remote covers, typically fall within the 40A to 60A range. This hardness level offers enough softness for shock absorption and grip, while being firm enough to keep their shape.
Household items like toothbrush handles, placemats, and cup lids vary from 40A to 70A, depending on the needed grip, texture, and support.
Industrial Applications: Emphasizing Performance and Environmental Adaptation
Industrial silicone must handle pressure, heat, vibration, and wear.
The recommended hardness here ranges from 50A to 90A, with Shore D used for more rigid parts.
Seals such as O-rings, gaskets, and sealing strips commonly have hardness between 50A and 70A. They need the right hardness to maintain a tight seal under pressure and avoid leaks, and higher hardness is preferred for harsh environments.
Damping pads and buffers usually fall between 50A and 65A, offering enough softness to absorb shock while remaining strong enough to resist deformation.
Cable insulation and electrical potting materials vary widely in hardness, depending on their function, but focus on insulation, heat resistance, and durability.
Industrial rollers and conveyor belts often require hardness of 70A or higher, sometimes even Shore D, to provide excellent strength, abrasion resistance, and stability under heavy loads.
Structural Components & Composite Materials: Hardness for Support
When silicone is part of a structure or layered with other materials, it must stay firm and stable.
For these applications, the recommended hardness is 70A or above, or Shore D.
Hard buttons or keycaps need to offer clear tactile feedback and durability, typically using silicone with hardness between 70A and 85A.
Internal support components require even higher hardness, usually between 80A and 90A, or Shore D, to maintain shape and resist forces.
For silicone overmolding on tools or devices, hardness depends on the needed grip and function. Tool handles often use silicone with hardness between 60A and 80A, balancing comfort with strength and durability.
Conclusion
Shore hardness is more than just a number. It’s a crucial factor that shapes how silicone feels, performs, and functions in real-world use. By understanding the different hardness levels and how they relate to specific needs, you can make smarter, more effective material choices.
With decades of experience in silicone manufacturing, we have the expertise and technology to produce high-quality, high-performance silicone products tailored to your needs. Whether you’re creating medical devices, consumer goods, or industrial components, we can help you bring your ideas to life with precision and reliability. Contact us today to start your custom silicone solution.
