Types de silicone : propriétés, différences et applications

Silicone is not a single material. It is a broad family of polymer materials that can be formulated into liquids, gels, pastes, foams, flexible elastomers, and solid rubber products. Changes in molecular structure, fillers, curing chemistry, and processing method can produce silicone materials with very different mechanical, thermal, and chemical characteristics.

For engineers and product designers, understanding the different types of silicone is important because a silicone selected for sealing a housing may not be suitable for a fuel-system gasket, an injection-molded medical component, or a high-temperature industrial part.

Four of the most commonly discussed types of silicone rubber are:

• Room-Temperature-Vulcanizing Silicone (RTV)
• Liquid Silicone Rubber (LSR)
• Fluorosilicone
• High-Consistency Rubber (HCR)

These silicone types differ in material state, curing method, chemical resistance, manufacturing process, cost, and typical applications. Understanding these differences makes it easier to select an appropriate silicone for a specific engineering environment.

What Is Silicone?

Silicone is a family of polymers based around a silicon-oxygen backbone. Depending on the formulation, the material can be produced in forms ranging from low-viscosity fluids to flexible rubber and relatively firm solid elastomers.

Silicone materials are widely valued for characteristics such as flexibility, resistance to environmental degradation, useful performance over a broad temperature range, and the ability to be formulated for specialized applications. However, these properties should not be treated as identical across every silicone grade.

The actual performance of a silicone product depends on several factors, including:

• Polymer formulation
• Curing system
• Fillers and additives
• Material hardness
• Exposure temperature
• Chemical environment
• Manufacturing process

For this reason, simply specifying “silicone” on an engineering project is often not enough. The required silicone type and grade should match the operating conditions of the finished component.

What Are the Main Types of Silicone?

Silicone manufacturers produce hundreds of formulations, but four categories are particularly useful when discussing common silicone rubber materials: RTV silicone, liquid silicone rubber, fluorosilicone, and high-consistency rubber.

1. Room-Temperature-Vulcanizing Silicone (RTV)

Room-temperature-vulcanizing silicone, usually shortened to RTV silicone, is formulated so that it can cure into its final elastomeric state without requiring a high-temperature curing process.

RTV silicone is commonly divided into two categories: RTV-1 and RTV-2.

RTV-1 Silicone

RTV-1 is a one-component silicone system supplied ready for use. After application, the curing process begins when the material reacts with moisture in the surrounding air.

Different cross-linking systems can be used. Depending on the formulation, small quantities of substances such as acetic acid, alcohols, or amines may be released during curing, while other formulations use different curing chemistry.

RTV-1 is particularly useful where convenient application is important. Typical applications include:

• Sealants
• Bonding applications
• Protective coatings
• Gap sealing
• General-purpose industrial sealing

Because it does not require mixing immediately before use, RTV-1 is often selected for relatively straightforward sealing and bonding operations.

RTV-2 Silicone

RTV-2 is a two-component silicone system. The two components are mixed before application, after which the curing process begins.

RTV-2 generally cures faster after mixing than RTV-1 and is available in a wider range of formulations. Depending on the material, RTV-2 may use a condensation-curing system or a platinum-catalyzed curing system.

Platinum-cured formulations are particularly useful where curing byproducts need to be minimized.

RTV-2 silicone is commonly associated with applications such as:

• Mold making
• Revêtements
• Casting-related processes
• Prototype manufacturing
• Specialized industrial applications

RTV-1 vs. RTV-2

The main difference is the number of components and the way they are prepared for use. RTV-1 is supplied as a single ready-to-use material and typically relies on environmental moisture for curing. RTV-2 requires two components to be mixed before application.

For simple sealing and bonding, RTV-1 can be convenient. When controlled curing, mold production, or broader formulation options are required, RTV-2 may be more appropriate.

2. What Is Liquid Silicone Rubber (LSR)?

Liquid Silicone Rubber, ou LSR, is generally supplied as a two-part, platinum-cured silicone raw material. One of its most important characteristics is its relatively high fluidity before curing.

This flowability allows the uncured material to enter small mold features and reproduce fine details. As a result, LSR is widely associated with precision injection molding and the production of complex molded silicone parts.

Common LSR applications include:

• Seals
• Gaskets
• Precision molded components
• Electronic potting applications
• Medical components using qualified grades
• Food-contact products using appropriately certified grades

The platinum curing process does not generate the same curing byproducts associated with some condensation-curing silicone systems. This is one reason suitable LSR formulations are widely used for applications where cleanliness and controlled material performance are important.

However, the term “LSR” does not automatically mean that every liquid silicone rubber is approved for medical or food-contact use. Regulatory suitability depends on the specific material grade, manufacturing conditions, testing requirements, and applicable certification.

3. What Is Fluorosilicone?

Fluorosilicone is a modified silicone material designed to provide improved resistance to certain fuels, oils, and organic solvents.

Conventional silicone and fluorosilicone share a similar silicon-oxygen polymer backbone. In fluorosilicone, however, some of the chemical groups attached to the polymer chain are replaced with fluorinated groups. This modification improves the material’s behavior in chemical environments that can be difficult for conventional silicone.

Fluorosilicone is particularly valued for resistance to substances such as:

• Fuel
• Huile
• Certain solvents
• Hydrocarbon-based fluids

This makes fluorosilicone especially useful in industries where elastomer seals may encounter aggressive fluids.

Les applications typiques comprennent :

• Automotive sealing components
• Aerospace seals
• Fuel-system seals
• Oil-resistant gaskets
• Components exposed to selected organic solvents

Fluorosilicone should not be considered universally better than conventional silicone. Its improved chemical resistance comes with trade-offs. It is generally more expensive, and conventional silicone may provide better performance in some hot-air environments.

When Should You Choose Fluorosilicone Instead of Silicone?

Fluorosilicone becomes particularly attractive when a seal, gasket, or flexible component will experience sustained exposure to fuels, oils, or compatible organic solvents.

If the main requirements are general flexibility, environmental resistance, and sealing performance without significant fuel or solvent exposure, a conventional silicone formulation may be more economical.

The material should therefore be selected according to the actual operating environment rather than simply choosing the highest-performance formulation available.

4. What Is High-Consistency Rubber (HCR)?

High-Consistency Rubber, commonly called HCR, high-consistency silicone rubber, solid silicone, or gum stock, is a silicone material based on high-molecular-weight polysiloxane chains.

Before final processing, HCR generally has a relatively solid, gum-like consistency compared with liquid silicone rubber.

Fillers and other ingredients can be incorporated into HCR formulations to modify characteristics such as:

• Dureté
• Résistance à la chaleur
• Mechanical behavior
• Processing characteristics

HCR can be cured using peroxide-based systems or platinum-catalyzed systems. It is commonly supplied as bulk raw material, including bars, tubes, cylinders, and other stock forms that are processed into finished silicone components.

Typical HCR applications include:

• Seals
• Gaskets
• Tubulures
• Automotive components
• Household products
• Qualified medical components

HCR is often described as “solid silicone,” but the terminology can create confusion. HCR describes an important material and processing category, whereas “solid silicone” may also be used more generally to describe a cured silicone product that is no longer in liquid, paste, gel, or foam form.

RTV vs. LSR vs. Fluorosilicone vs. HCR

A practical selection approach is:

• Choose RTV for sealing, bonding, coating, and many mold-making applications.
• Choose LSR for repeatable precision molding and complex molded silicone parts.
• Choose fluorosilicone when fuel, oil, or certain solvent exposure is a major design requirement.
• Choose HCR for traditional solid silicone rubber products and applications requiring a gum-stock processing route.

What Forms Does Silicone Come In?

One common source of confusion is that a silicone type and a silicone form are not necessarily the same thing.

Terms such as RTV, LSR, HCR, and fluorosilicone primarily describe material chemistry, curing behavior, or processing categories. Terms such as oil, grease, gel, foam, and emulsion often describe the physical form in which a silicone material is supplied or used.

Silicone Emulsion

A silicone emulsion consists of silicone material dispersed in a stabilized water-based system. Silicone emulsions can be used in lubricants, release agents, cleaners, and polishing products where easy spreading and controlled application are useful.

Silicone Oil

Silicone oils are generally based on relatively simple linear polysiloxane chains. Their fluid behavior makes them suitable for lubrication and fluid applications.

They can also serve as raw materials for further silicone formulations.

Liquid Silicone

The term liquid silicone broadly describes silicone in a fluid state. It should not always be treated as synonymous with LSR.

Liquid Silicone Rubber has a more specific industrial meaning and commonly refers to a two-part silicone raw material used for precision molding and related applications.

Silicone Caulk

Silicone caulk is typically a viscous RTV silicone product designed primarily for sealing joints and gaps.

Its combination of workability, adhesion, and environmental durability makes it common in construction, equipment sealing, and general maintenance applications.

Silicone Resin

Silicone resins generally form highly cross-linked structures after curing. They can be used in applications including:

• Adhesives
• Protective coatings
• Water-repellent coatings
• Heat-resistant coating systems

Silicone Grease

Silicone grease is produced by combining silicone oil with fillers to create a thicker lubricant-like material.

Applications may include lubrication, moisture protection, mold release, protection of electrical contacts, and sealing of selected joints.

Silicone Gel

Silicone gels are soft, gel-like materials that can be produced from two-component silicone systems and modified with additional ingredients to achieve the required consistency.

Their soft structure makes them suitable for applications where cushioning, conformability, encapsulation, or gentle contact with surrounding surfaces is required.

Silicone Foam

Silicone foam contains a cellular structure rather than being completely solid. Both open-cell and closed-cell foam structures can be produced depending on the manufacturing process and formulation.

Common applications include:

• Gaskets
• Entretoises
• Gap filling
• Insulation
• Compressible sealing components

Solid Silicone

Solid silicone generally describes cured silicone rubber with relatively long polymer chains and high molecular weight. In many engineering contexts, the term is closely associated with high-consistency rubber.

Finished products can include:

• Tubulures
• Engine mounts
• Seals
• Gaskets
• Flexible molded components

Silicone Type vs. Silicone Form: What Is the Difference?

Understanding this distinction can prevent material-selection mistakes.

A silicone type usually tells you more about the chemistry, curing system, raw-material condition, or intended manufacturing route. Examples include RTV silicone, LSR, fluorosilicone, and HCR.

A silicone form often describes the physical condition or delivery format of the material, such as:

• Huile
• Grease
• Gel
• Foam
• Emulsion
• Paste
• Solid

These categories can overlap. For example, LSR is liquid before curing but becomes an elastomeric solid after molding. RTV may be supplied as a paste or liquid and later cure into rubber.

Therefore, engineers should avoid choosing materials based only on whether they are described as “liquid,” “solid,” or “foam.” The underlying silicone chemistry and specific grade remain important.

Liquid Rubber vs. Liquid Silicone Rubber

Liquid rubber is a broad term and does not necessarily mean silicone.

A product marketed as liquid rubber may use silicone chemistry, but it may also be based on another elastomeric material such as polyurethane.

Liquid Silicone Rubber (LSR), on the other hand, specifically refers to a silicone-based material system. LSR is commonly associated with precision injection molding, sealing, bonding, and production of flexible molded components.

This distinction is particularly important when purchasing raw materials. A product described simply as “liquid rubber” should not be assumed to have the same temperature resistance, chemical behavior, curing characteristics, or processing requirements as LSR.

How to Choose the Right Type of Silicone

Material selection should start with the requirements of the final product rather than with a preferred silicone name.

1. Operating Temperature

Determine the expected continuous operating temperature as well as any short-duration temperature peaks.

A material that performs adequately at room temperature may behave differently when continuously exposed to elevated temperatures. Actual allowable temperatures should therefore be confirmed using data for the specific silicone grade.

2. Chemical Exposure

Identify every fluid or chemical that may contact the silicone component, including:

• Fuel
• Lubricating oil
• Hydraulic fluids
• Agents de nettoyage
• Solvents
• Process chemicals

Where fuel and oil resistance are critical, fluorosilicone may deserve consideration. Where aggressive chemical exposure is absent, specifying fluorosilicone may add unnecessary material cost.

3. Mechanical Requirements

A silicone component may need to withstand compression, stretching, repeated deformation, assembly forces, or long-term sealing pressure.

Important properties can therefore include:

• Dureté
• Flexibilité
• Tear resistance
• Compression behavior
• Recovery after deformation

The required values should be defined for the specific application rather than assuming that all silicone rubber behaves similarly.

4. Manufacturing Process

The intended manufacturing process can strongly influence material selection.

Common silicone processing routes include:

• Moulage par injection
• Compression molding
• Coulage
• Extrusion
• Revêtement
• Sealant application

LSR, for example, is particularly suitable for controlled molding processes where high material flow is useful, while RTV systems are more commonly associated with curing after application or casting.

5. Part Geometry

Thin walls, small channels, fine molded details, and complex cavities can affect both silicone selection and tooling design.

Highly flowable materials may be advantageous when a mold contains fine details, while other silicone forms may be better suited for extruded profiles, gaskets, or relatively simple solid components.

6. Regulatory Requirements

Medical and food-related projects require particular care.

It is incorrect to assume that all silicone is automatically food-safe or medical-grade. Suitability depends on the exact material grade, supporting documentation, manufacturing environment, applicable standards, and the final intended use.

7. Production Volume

Prototype quantities and large-volume production may favor different manufacturing strategies.

For an early prototype, casting or RTV-based processing may sometimes provide a practical route. For repeat production of detailed silicone components, a controlled molding process such as LSR injection molding may offer better repeatability.

8. Cost

More specialized does not always mean more suitable.

Fluorosilicone, for example, offers valuable chemical resistance but is more expensive than conventional silicone. If the finished part will never encounter fuels, oils, or relevant solvents, that additional performance may not justify the higher material cost.

Applications of Different Silicone Types

Automobile

Silicone materials are used throughout automotive systems for sealing, insulation, flexible connections, gaskets, and temperature-resistant components.

Where parts encounter fuel or oil, fluorosilicone may be selected for suitable seals and gaskets. In other areas, conventional silicone compounds may provide an appropriate balance of flexibility, durability, and cost.

Aérospatial

Aerospace components can combine demanding temperature, sealing, and chemical-exposure requirements. Fluorosilicone is particularly relevant where elastomer components may contact fuels or oils.

Material qualification remains essential because aerospace applications generally require tightly controlled material properties and manufacturing documentation.

Applications médicales

Qualified silicone grades can be used for medical components such as tubing, seals, molded parts, and other flexible devices.

LSR and HCR can both be found in medical manufacturing, depending on the component and material specification.

However, material suitability must be confirmed for each application. A generic silicone grade should never be assumed to meet medical requirements solely because other silicone materials are used in medical products.

Électronique

Silicone may be used for potting, insulation, moisture protection, sealing, protective coatings, and flexible components around electronic assemblies.

Different forms such as gels, greases, liquids, coatings, and molded elastomers make silicone useful across a wide range of electronic designs.

Produits de consommation

Silicone rubber appears in many household and consumer applications, including flexible seals, kitchen-related components, protective elements, and molded products.

Industrial Equipment

Industrial machines commonly use silicone for sealing, gaskets, insulation, vibration-related components, and protective applications.

The best material depends on temperature, pressure, chemical exposure, geometry, and required service life.

Silicone Components and Precision Manufacturing

Silicone parts rarely function in isolation. A seal, gasket, diaphragm, molded elastomer, or O-ring often operates together with precision-machined metal or engineering-plastic components.

Examples include:

• Aluminum housings containing silicone seals
• Stainless steel valve bodies with sealing grooves
• CNC-machined covers with silicone gaskets
• Precision shafts passing through elastomer seals
• Machined fixtures and tooling used during silicone component production
• Plastic or metal inserts used together with molded elastomers

In these assemblies, the performance of the silicone component can depend just as much on the geometry of the mating CNC part as on the silicone material itself.

Seal Groove Geometry

A groove that is too deep, too shallow, too narrow, or incorrectly positioned can prevent a silicone seal from achieving the intended compression.

Groove dimensions should therefore be controlled according to the seal design rather than treated as non-critical machining features.

Finition de surface

The finish of the mating surface can influence sealing behavior. Rough machining marks, scratches, sharp burrs, or surface defects may create potential leakage paths or damage an elastomer during assembly.

When sealing performance is critical, surface-finish requirements should be included in the drawing and reviewed together with dimensional tolerances.

Edge Conditions

Sharp edges can cut or scrape silicone seals during assembly. Appropriate chamfers, radii, and deburring can help reduce the risk of installation damage.

Dimensional Tolerance

Housing diameter, groove width, groove depth, shaft diameter, flatness, and alignment can all influence seal compression and assembly fit.

This is why silicone selection and CNC component design should be considered as part of the same mechanical system.

Tuofa CNC Allemagne supports custom precision manufacturing for prototype and production components, including CNC-machined metal and engineering-plastic parts that interface with silicone seals, gaskets, molded elastomers, and other flexible components.

For assemblies involving silicone sealing elements, manufacturing review can focus on details such as groove geometry, mating surfaces, tolerances, chamfers, surface finish, and assembly fit before machining begins.

Frequently Asked Questions About Silicone Types

What are the four main types of silicone?

Four commonly discussed types of silicone rubber are RTV silicone, Liquid Silicone Rubber (LSR), fluorosilicone, and High-Consistency Rubber (HCR). Each has different curing behavior, processing characteristics, and typical applications.

What is the difference between RTV and LSR silicone?

RTV silicone cures at room temperature and is widely used for sealing, bonding, coatings, casting, and mold-making applications. LSR is typically a two-part, platinum-cured, highly flowable silicone raw material used for precision molding and molded silicone components.

Is liquid silicone the same as silicone rubber?

Not necessarily. “Liquid silicone” can broadly describe silicone in liquid form, while Liquid Silicone Rubber refers to a more specific silicone rubber material system used for molding and related manufacturing processes.

Is fluorosilicone better than regular silicone?

Fluorosilicone is not universally better. Its main advantage is improved resistance to fuels, oils, and certain organic solvents. Conventional silicone may be more economical and may perform better in some hot-air environments.

What is solid silicone called?

Solid silicone rubber is often associated with High-Consistency Rubber (HCR), also known as gum stock. However, “solid silicone” can also be used more generally to describe silicone that has cured into a solid elastomeric product.

What type of silicone is commonly used for molds?

Two-component RTV silicone, particularly RTV-2 formulations, is widely associated with mold-making applications. The correct grade depends on mold geometry, required flexibility, curing method, casting material, and expected production life.

Which silicone is best for fuel resistance?

Fluorosilicone is commonly selected when resistance to fuels, oils, and certain organic solvents is an important design requirement.

Is all silicone food safe?

No. Silicone as a material family is widely used in food-related products, but food-contact suitability depends on the specific formulation, grade, manufacturing process, and applicable certification.

Is all silicone medical grade?

No. Only specifically qualified silicone grades should be used for applications requiring medical compliance. The requirements vary depending on whether the silicone is used for external contact, short-term contact, long-term implantation, or another medical application.

Conclusion

There is no single “best” silicone for every application.

RTV silicone is particularly useful for sealing, bonding, coating, casting, and mold-making. Liquid Silicone Rubber is well suited to precision molded components and detailed geometries. Fluorosilicone becomes valuable when exposure to fuels, oils, and certain solvents is a major concern. High-Consistency Rubber remains an important option for traditional solid silicone rubber products.

It is also important to distinguish silicone types from silicone forms. Oils, gels, greases, foams, emulsions, liquids, and solids describe how silicone may be supplied or used, but they do not completely define the underlying material chemistry or performance.

The final material choice should consider operating temperature, chemical exposure, mechanical requirements, manufacturing method, part geometry, regulatory requirements, production volume, and cost.

For products in which silicone seals, gaskets, or molded elastomers interface with precision metal or plastic components, the mating parts should also be designed carefully. Groove dimensions, sealing surfaces, tolerances, edge conditions, and surface finish can directly affect assembly and sealing performance.

Need precision-machined components for an assembly using silicone seals or elastomer parts? Tuofa CNC Germany can review your CAD drawings, tolerances, material requirements, and sealing interfaces and provide CNC machining support for prototype and production components.