Why is silicone so chemically resistant?
In a recent article, we looked at why silicone handles heat and cold so well. But there’s another reason it’s trusted in so many demanding environments and that’s its exceptional chemical resistance.
Put simply, chemical resistance is a material’s ability to withstand exposure to harsh substances; from cleaning agents to acids, alkalis, solvents and more, without breaking down, swelling, cracking or losing its function.
This quality is vital in industries like pharmaceuticals, food production, medical and dairy systems, where equipment is regularly exposed to aggressive cleaning fluids and reactive compounds. If tubing, gaskets or seals begin to degrade, it can lead to contamination, equipment failure or expensive downtime.
So why is silicone chemically resistant? Why doesn’t it break down when other materials do? To answer that, we need to take a look at the unique molecular structure that sets silicone apart from most other rubbers and why that structure makes it one of the most chemically stable materials in use today.
What Does “Chemical Resistance” Actually Mean?
Before we get into why silicone is so chemically resistant, let’s first explain what that means in practice.
When a material comes into contact with a chemical, whether it’s a detergent, acid, solvent or even water, there’s a risk that the material will react with it. This can lead to:
- Swelling
- Softening or hardening
- Cracking or brittleness
- Discolouration
- Loss of strength or flexibility
These kinds of changes mean the material is starting to break down at a molecular level, even if it still looks fine on the surface. Over time, this can affect how well a seal works, how clean a fluid path stays or how safe a product is to use.
A chemically resistant rubber like silicone is designed to resist this kind of attack. It doesn’t absorb or react with most chemicals, which means it stays stable, strong and flexible even after repeated exposure to harsh cleaning agents or active compounds.
That’s why silicone is often used in pharmaceutical systems, medical devices, food and beverage equipment and other environments where chemical contact is unavoidable.
But what makes silicone so different from other rubbers? To understand that, we need to take a closer look at what it’s made of.
The Molecular Structure of Silicone: Built to Resist
Most rubbers, like natural rubber or nitrile , are made from organic polymers, which means their molecular backbone is built from carbon-carbon (C–C) bonds. These carbon chains are flexible and versatile, but they’re also more reactive. Exposure to heat, oxygen or chemicals can cause those carbon bonds to break apart or rearrange, leading to degradation over time.
Silicone is different. Its backbone is made from silicon and oxygen atoms (Si–O bonds) – a structure more like glass than plastic. This small change has a huge impact.
The Si–O bond is much stronger than a C–C bond, and here’s why:
- Oxygen is highly electronegative, meaning it pulls electrons toward itself strongly
- Silicon is more electropositive, so it readily shares electrons
- This creates a very strong bond with high stability
In technical terms, the bond energy of Si–O is around 444 kJ/mol, while a C–C bond is only about 348 kJ/mol. That means it takes a lot more energy, from heat or aggressive chemicals, to break the silicone structure. This is one of the core reasons silicone rubber is so chemically resistant.
The Si–O bond also forms a wide bond angle, creating a flexible, open structure. This gives silicone its famous elasticity while keeping its chemical stability; a rare combination in rubber materials.
Think of silicone like a springy glass chain: flexible enough to bend without snapping, but chemically tough enough to resist attack. That’s the foundation of its exceptional chemical compatibility and why it outlasts many other rubbers in harsh environments.
Why Silicone Doesn’t React: Stability by Design
So what exactly stops silicone from reacting with chemicals in the first place? There are a few key reasons why silicone is considered an inert and chemically resistant material:
1. Strong Si–O Bonds Resist Breakage
As we covered earlier, the silicon–oxygen bonds in silicone are much harder to break than carbon–carbon bonds. That makes the entire structure more resistant to chemical attack, even under heat or pressure.
2. Wide Bond Angles = Less Strain
The angles between atoms in a silicone chain are wider than in most organic polymers. This “looser” structure reduces internal stress, making it less likely for chemical energy to disrupt the bonds.
3. Hydrophobic Surface (Water-Repellent)
Silicone has a naturally hydrophobic (water-repellent) surface, and the reason lies in its molecular structure.
Each silicon atom in the backbone is bonded not just to oxygen, but also to methyl groups (–CH₃), which are small, non-polar hydrocarbons. These methyl groups form the outer surface of the material. Since water is polar and methyl groups are non-polar, they don’t mix, so water and many polar chemicals are repelled. That’s why liquids bead up on silicone instead of soaking in.
This surface behaviour is a big part of what helps silicone resist chemical absorption, swelling or breakdown, especially in pharma and food environments where tubing and seals are regularly exposed to water-based cleaning agents or sanitising fluids.
4. No Active Reaction Sites
Many other rubbers contain what chemists call “reaction sites”; specific points in the molecular structure that are vulnerable to attack by chemicals, heat or oxygen.
These might include:
- Double bonds (two carbon atoms sharing two electrons)
- Sulphur bridges (crosslinks used in vulcanised rubbers)
- Polar functional groups that easily interact with other molecules
These sites act like open doors for chemical reactions, places where external chemicals can interact with and break down the material.
Silicone doesn’t have these. Its Si–O backbone is fully bonded and stable, and the methyl groups on the outside are non-reactive. That means there are no obvious weak points for chemicals to attack; helping silicone stay inert, stable, and long-lasting, even in harsh environments.
Together, these properties make silicone one of the most chemically stable rubbers available and a top choice for fluid contact applications in sensitive or sterile environments.
When Silicone Does React (And How to Avoid It)
Silicone rubber is incredibly chemically stable but like any material, it has its limits.
While it resists most chemicals extremely well, there are certain substances and conditions that can slowly break it down, cause swelling, or lead to permeation over time.
Here’s what to watch out for:
1. Strong Acids and Bases
Silicone performs well in many pH ranges, but high concentrations of strong acids (like nitric acid) or strong bases (like sodium hydroxide) can eventually attack the siloxane bonds, especially at high temperatures or over long exposure times.
2. Swelling in Some Organic Solvents
Although silicone is resistant to chemical attack, it can still absorb certain non-polar solvents like benzene, toluene or hexane. This doesn’t destroy the material immediately, but it can cause swelling, softening, or changes in flexibility, especially in dynamic applications like seals or tubing.
3. Permeation
Silicone is a permeable material, meaning that over time, small molecules can slowly pass through it, especially gases and some solvents. This can affect barrier properties in ultra-sensitive applications, like pharmaceutical packaging or sealed fluid lines.
4. Compatibility with Some Oils
Silicone resists most oils and greases, but swelling can occur with certain hydrocarbon-based or silicone-based oils, depending on the compound formulation.
So How Do You Avoid These Issues?
The key is choosing the right grade of silicone for the environment it will be used in. At Silclear, we tailor our silicone compounds for specific resistance needs, taking into account:
- Chemical exposure (type, strength, duration)
- Temperature
- Mechanical stress
- Sterilisation methods (e.g. steam, CIP, SIP)
If there’s any doubt, it’s always worth checking chemical compatibility charts or asking us directly, we’re happy to help you choose the most suitable material for your application.
Why Chemical Resistance Matters in Critical Applications
In industries where hygiene, purity, and performance are non-negotiable, chemical resistance isn’t just a bonus, it’s essential!
Whether you’re producing pharmaceuticals, food, drink, dairy, cosmetics or biotechnology products, your equipment is exposed to cleaning agents, sterilisation fluids, and sometimes the materials being processed themselves. If a seal, gasket or tube starts to degrade, even slightly, it can lead to:
- Contamination of the product
- Equipment failure or leakage
- Health and safety risks
- Regulatory issues and production downtime
This is where silicone shines.
Because of its chemical stability, flexibility and clean performance, silicone is trusted in critical environments that demand both safety and reliability. It can:
- Resist aggressive cleaning agents
- Withstand repeated sterilisation using steam or chemicals (CIP/SIP)
- Avoid swelling or cracking, even with repeated exposure
- Minimise extractables and leachables in sensitive applications
- Hold its shape and seal integrity without becoming brittle
From pharma-grade sterile tubing to food-grade pump gaskets and dairy processing lines, silicone plays a vital role in keeping systems clean, safe, and operational over the long term.
Its resistance to both heat and chemicals makes it an ideal choice wherever cleanliness, performance, and compliance matter most.
Contact Silclear for chemically resistant silicone
Silicone’s chemical resistance isn’t just luck, it’s built into its very structure.
Thanks to its strong Si–O backbone, non-reactive surface, and lack of vulnerable reaction sites, silicone rubber stands up to the harshest cleaning agents, solvents, and sterilisation conditions where other materials would fail.
That’s why it’s used everywhere from pharma cleanrooms to food production lines, biotech labs to dairy parlours; any setting where performance, purity and long-term reliability matter.
At Silclear, we’ve spent decades formulating and manufacturing chemically resistant silicone tubing, seals, mouldings and components for customers across these industries. If you need materials that can handle the pressure (and the chemicals), we’re here to help.
Call us on +44 (0)1425 610700, email info@silclear.com or enquire below.
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