Types of Silicone Rubber: RTV vs. HCR vs. LSR
Reading Time: 5 minutes
Last Updated on August 20, 2026
For industries such as automotive, aerospace and healthcare, products must perform reliably, withstand demanding conditions and meet specific manufacturing and performance requirements. Because of this, manufacturers often turn to long-lasting, durable materials such as silicone rubber.
Silicone rubber is flexible at low temperatures and resistant to heat and aging. It is easy to process and has good mechanical properties that remain stable over a wide temperature range.
There are three main types of silicone rubber: room-temperature-vulcanizing silicone (RTV), high-consistency silicone rubber (HCR) and liquid silicone rubber (LSR). Although they share many of silicone’s inherent performance advantages, they differ in consistency, curing methods, processing requirements and suitability for different production volumes and applications.
Choosing among these types of silicone rubber depends on factors such as the application, manufacturing process, production volume, part geometry and performance requirements.
This blog compares RTV, HCR and LSR, including how they cure, how they are processed, common applications and factors to consider when selecting the right silicone rubber for your project.
What Are the Main Types of Silicone Rubber?
The three main types of silicone rubber are RTV, HCR and LSR:
- RTV (room-temperature-vulcanizing silicone) cures at room temperature and is commonly used for sealing, bonding, coating and mold-making applications.
- HCR (high-consistency silicone rubber) is a solid silicone rubber cured at elevated temperatures and processed through methods including extrusion, calendering, compression molding and injection molding.
- LSR (liquid silicone rubber) is a low-viscosity, two-component material particularly well suited to automated injection molding, complex geometries and high-volume production.
The best type depends on how the component will be manufactured and the performance required from the finished product.
What Is RTV Silicone Rubber?
As the name implies, room-temperature-vulcanizing silicone (RTV) cures at room temperature to form a highly elastic silicone rubber. RTV is available as a one-component (RTV-1) or two-component (RTV-2) system.
RTV-1 Silicone
RTV-1 is a one-component system that cures when exposed to atmospheric moisture. There are four different technologies available with unique properties to suit a wide variety of applications.
The material cures from the outside in, so it forms a skin first and then cures through the silicone. RTV-1 silicones are commonly used for sealing, bonding and coating applications.
RTV-2 Silicone
RTV-2 silicone elastomers are two-part, pourable or mixable materials that start to cure at room temperature shortly after mixing. Some RTV-2 materials use platinum curing and can also be heated to accelerate curing when faster cure and demolding are required.
Most RTV-2 silicones retain their full elasticity up to 180 °C, even after long-term exposure. Some products can withstand short-term heat exposure up to 300 °C.
Common RTV-2 applications include:
- Mold making
- Appliances
- Healthcare applications
- Lighting
- Electronics
Both RTV-1 and RTV-2 have a long shelf life of up to 12 months when stored at room temperature between 20 and 25 °C.
What is HCR Silicone Rubber?
High-consistency silicone rubber (HCR), also known as solid silicone rubber, is cured at high temperatures using either organic peroxides or a platinum catalyst. HCR contains long polymer chains with a high molecular weight, giving the material its solid consistency.
Because of its outstanding mechanical properties, HCR is used in a wide range of static and dynamic applications, including:
- Automotive
- Aerospace
- Electrical transmission and distribution
- Wire and cable
- Food processing
- Molded rubber goods
HCR provides excellent temperature and aging resistance. It can be processed using conventional methods such as:
- Extrusion
- Calendering
- Compression molding
- Injection molding
How Is HCR Silicone Cured?
HCR can be cured using organic peroxide or a platinum catalyst. The curing method can influence processing characteristics and properties of the finished silicone product.
Peroxide curing is a well-established free-radical process that offers good processing flexibility and is commonly used for mechanical rubber goods. Platinum curing, also known as addition curing, uses platinum as a catalyst and does not generate the residuals or volatile byproducts associated with peroxide curing.
Platinum-cured silicone can provide excellent transparency, high tensile and tear strength and high purity, making appropriate grades useful for demanding food, beverage and healthcare applications. The best curing system depends on the manufacturing process, required physical properties and end-use requirements. For a detailed comparison, read “Platinum Cured Silicone: Benefits, Applications and How It Compares to Peroxide Curing“.
What is Liquid Silicone Rubber (LSR)?
Liquid silicone rubber (LSR) is a thermoset rubber supplied as a two-part, colorless, translucent paste that provides good clarity and excellent mechanical strength.
This material offers unique characteristics that are not obtainable with conventional thermoplastic elastomers (TPEs). Once LSR is heated and crosslinked, its chemical and physical properties can no longer be altered. As a result, cured LSR maintains its physical and chemical properties over a broad range of temperatures and environmental conditions.
LSR has a lower viscosity than solid silicone rubber (HCR). Therefore, it is pumpable and can be supplied as a two-component, ready-to-use system. LSR is used in industries including:
- Automotive
- Electronics
- Electrical transmission and distribution
- Mechanical goods
- Medical devices
- Healthcare consumables
What Are the Advantages of LSR Injection Molding?
Injection molding with LSR can produce highly consistent parts and reproduce intricate, complex geometries. Because LSR has a low viscosity, it can fill very small spaces in a mold, making it useful for complex components such as those found in medical and electronic applications.
LSR is also well suited to high-volume manufacturing. Automated injection molding can produce hundreds or thousands of parts with relatively little manual labor, helping manufacturers achieve consistent production at scale.
RTV vs. HCR vs. LSR: What’s the Difference?
RTV, HCR and LSR share many of silicone rubber’s performance advantages, but their material form, curing requirements, processing methods and ideal production volumes differ.
| Characteristic | RTV | HCR | LSR |
|---|---|---|---|
| Material form | One- or two-component material | High-consistency solid rubber | Low-viscosity, two-component liquid/paste |
| Curing | Cures at room temperature; some RTV-2 grades can be heat accelerated | High-temperature peroxide or platinum curing | Heat activated/crosslinked |
| Common processing | Sealing, bonding, coating, pouring/mold making | Extrusion, calendering, compression and injection molding | Automated injection molding |
| Typical production | Prototyping and smaller production runs | Smaller to medium production runs depending on process | High-volume production |
| Key advantage | Room-temperature curing and versatility | Excellent mechanical properties and processing flexibility | Complex geometries, tight tolerances and automation |
How Do You Choose the Right Type of Silicone Rubber?
RTV, HCR and LSR offer many of the same performance advantages, but the right silicone rubber depends on the component, manufacturing process and required production volume. Consider these questions when selecting among the different types of silicone rubber:
- How many parts need to be produced?
- Does the material need to be molded, extruded, poured, bonded or used as a coating?
- How complex is the component geometry?
- Are tight tolerances required?
- What mechanical and temperature properties are required?
- Does the application have specific food, healthcare or other regulatory requirements?
- Would peroxide or platinum curing be more appropriate for an HCR application?
Generally, RTV and HCR materials are better suited to smaller production runs, while LSR is ideal for high-volume manufacturing or tight tolerances because it can help reduce unit costs through automated processing.
Find the Right Type of Silicone Rubber for Your Application
Selecting the right type of silicone rubber requires balancing processing requirements, production volume and finished-part performance. H.M. Royal supplies a full line of WACKER silicone elastomers, including RTV, HCR and LSR materials, to meet a variety of manufacturing requirements.
If you need help selecting the right material for your application, contact H.M. Royal to discuss your requirements with a material expert. We provide a full line of Wacker silicone elastomers to meet your unique requirements.
Frequently Asked Questions About Types of Silicone Rubber
What are the three main types of silicone rubber?
The three main types of silicone rubber are RTV, HCR and LSR. RTV cures at room temperature, HCR is a high-consistency solid silicone cured at elevated temperatures, and LSR is a low-viscosity two-component silicone commonly used in automated injection molding.
What is the difference between RTV and LSR silicone?
RTV cures at room temperature and is commonly used for applications such as sealing, bonding, coating and mold making. LSR is a low-viscosity, two-component material that is heat-cured and particularly well suited to automated injection molding and high-volume production.
What is the difference between HCR and LSR?
HCR is a solid, high-consistency silicone that can be extruded, calendered, compression molded or injection molded. LSR has a much lower viscosity, is pumpable and is especially well suited to automated injection molding of complex parts and high-volume production.
Can HCR silicone be platinum cured?
Yes. HCR can be cured using either organic peroxides or a platinum catalyst. Platinum curing is an addition-curing process that does not generate residual or volatile curing byproducts and can provide excellent transparency and mechanical properties.
Which type of silicone rubber is best for injection molding?
Both HCR and LSR can be injection molded. LSR is particularly useful for high-volume automated production, complex shapes and tight tolerances because its low viscosity allows it to fill small spaces in the mold. HCR can also be injection molded and offers excellent mechanical properties.
Which silicone rubber is best for prototyping?
RTV is often a practical choice for prototyping and initial production because it cures at room temperature. As production demand increases, manufacturers may transition to HCR or LSR depending on the part and process requirements.
