What Are the Different Types of Silicone Rubber?
The most common types include:
HTV/HCR Silicone Rubber
LSR (Liquid Silicone Rubber)
RTV-1 (One-Part Room-Temperature Vulcanizing Silicone)
RTV-2 (Two-Part Room-Temperature Vulcanizing Silicone)
HTV/HCR Silicone Rubber
HTV stands for High Temperature Vulcanizing silicone rubber, while HCR stands for High Consistency Rubber.
These terms are commonly used for solid silicone rubber supplied in a gum-like form. HCR/HTV is typically processed using heat and pressure after mixing with an appropriate curing system.
Hailan describes HTV silicone rubber, also known as HCR, as a solid silicone material suitable for processes such as compression molding, transfer molding, and rubber injection molding.
HTV/HCR silicone rubber generally offers:
High temperature resistance
Good elasticity
Excellent weather resistance
Good electrical insulation
Good mechanical strength
Good resistance to UV and ozone
A wide range of hardness options
Good suitability for extrusion and molding
HTV/HCR can be processed through:
Compression molding
Transfer molding
Injection molding
Extrusion
Calenderin
HTV/HCR silicone rubber is widely used for:
Silicone seals and gaskets
O-rings
Automotive components
Cable and wire insulation
Electrical components
Silicone tubing
Silicone keypads
Kitchenware
Swim caps
Industrial molded parts
LSR – Liquid Silicone Rubber
LSR stands for Liquid Silicone Rubber.
Unlike HTV/HCR, which is supplied as a solid rubber compound, LSR is supplied as a liquid two-component system.
Typically, the two components are metered and mixed before being injected into a heated mold. A platinum-catalyzed addition-curing reaction then crosslinks the silicone into an elastic solid.
A typical LSR system consists of:
Part A
Silicone base
Platinum catalyst
Part B
Silicone base
Crosslinking components
The two components are accurately metered and mixed, then injected into a heated mold.
The material cures inside the mold and becomes a flexible silicone elastomer.
Hailan's technical information describes LSR as a two-component system and explains that it is suitable for liquid injection molding.
LSR is particularly attractive for automated, high-volume manufacturing because of its:
- Low viscosity
- Excellent flowability
- High dimensional consistency
- Fast curing
- Good transparency
- Good elasticity
- Excellent temperature resistance
- Good chemical and environmental resistance
- Suitability for complex geometries
LSR can also be used for insert molding and overmolding when the material and substrate are properly selected.
Medical components
Healthcare products
Baby-care products
Seals and gaskets
Valves and diaphragms
Automotive components
Electronic components
Electrical connectors
Kitchenware
Wearable products
Precision molded silicone parts
However, not every LSR grade is automatically medical-grade, biocompatible, or food-contact compliant. These properties depend on the specific formulation, manufacturing process, testing, and intended application.
For medical devices, FDA guidance recognizes ISO 10993-1 as a framework for evaluating biological responses based on factors such as the type, degree, frequency, and duration of body contact.
Related internal links:
RTV Silicone Rubber
RTV stands for Room-Temperature Vulcanizing silicone rubber.
Unlike HTV, RTV silicone can cure at or around room temperature, depending on the formulation and curing mechanism.
RTV silicone is commonly divided into:
RTV-1
RTV-2
RTV-1 Silicone Rubber
RTV-1 is a one-component, ready-to-use silicone system.
It normally cures through exposure to moisture in the air. Once applied, curing starts at the surface and progresses inward.
Depending on the chemistry, different curing byproducts may be released during the curing process.
Sealing
Bonding
Coating
Waterproofing
Electronic protection
Construction applications
Automotive sealing
Appliance sealing
The biggest advantage of RTV-1 is convenience.
The material is supplied as a ready-to-use product, so the user generally does not need to perform the same two-component metering and mixing operation required by RTV-2 or many LSR systems.
RTV-2 Silicone Rubber
RTV-2 is a two-component room-temperature curing silicone system.
The two components are mixed before application. Once mixed, a chemical reaction causes the silicone to crosslink and form an elastomer.
Depending on the chemistry, RTV-2 systems can use different curing mechanisms, such as condensation or addition curing.
Silicone molds
Prototyping
Encapsulation
Potting
Industrial sealing
Electronic protection
Coating
Casting applications
One advantage of RTV-2 is that it can provide greater flexibility in formulation and processing compared with ready-to-use one-component systems
HTV vs. LSR vs. RTV: What Is the Difference?
| Property | HTV/HCR | LSR | RTV-1 | RTV-2 |
|---|---|---|---|---|
| Physical form | Solid/gum-like | Liquid | Paste/liquid | Liquid/paste |
| Components | Usually compound + curing system | Two components | One component | Two components |
| Typical curing | Heat curing | Heat curing | Moisture curing | Room-temperature curing |
| Typical process | Compression, transfer, extrusion | Injection molding | Dispensing/application | Mixing + casting/dispensing |
| Automation | High | Very high | Medium | Medium |
| Complex parts | Good | Excellent | Limited | Good |
| High-volume molding | Good | Excellent | Limited | Moderate |
| Typical use | Molded/extruded products | Precision molded products | Sealing/bonding | Molding/encapsulation |
The exact processing conditions vary significantly by formulation, so this table should be treated as a general material-selection guide rather than a processing specification.
How Do You Choose the Right Silicone Rubber?
Selecting silicone rubber should start with the finished product requirements, rather than simply choosing the material with the highest specification.
Consider the following factors.
Compression molding → HTV/HCR
Silicone extrusion → HTV/HCR
High-volume precision injection molding → LSR
Sealing and bonding → RTV
Prototype silicone mold → RTV-2
The processing equipment available at the factory is also an important consideration.
Silicone rubber is available in a wide range of hardness levels.
Depending on the application, manufacturers may need:
Soft silicone for flexible products
Medium-hardness silicone for seals
Higher-hardness silicone for structural components
Hardness should not be evaluated alone.
Other important properties include:
Tensile strength
Elongation
Tear strength
Compression set
Rebound resilience
Temperature resistance
For example, Hailan's general-purpose molding silicone rubber is available across multiple Shore A hardness levels, demonstrating how one silicone family can be formulated for different mechanical requirements.
Silicone is often selected when the application requires resistance to elevated or low temperatures.
However, temperature resistance is grade-specific.
The actual operating environment should be considered, including:
Continuous temperature
Peak temperature
Temperature cycling
Heating time
Cooling conditions
Always verify the manufacturer's TDS before final material selection.
Consider exposure to:
Water
Humidity
UV radiation
Ozone
Oils
Fuels
Cleaning agents
Solvents
Chemicals
Silicone generally has good resistance to many environmental conditions, but it should not be assumed to be compatible with every chemical or fluid.
For products used in food, healthcare, or medical applications, certification and regulatory requirements can be especially important.
However, there is an important distinction:
A silicone material being described as "food grade" or "medical grade" does not automatically mean that every finished product made from it complies with every applicable regulation.
For food-contact applications, FDA explains that food-contact substances may be subject to specific authorization requirements depending on their intended use.
For medical devices, FDA recognizes ISO 10993-1 as an important framework for biological evaluation based on the device's nature and duration of contact with the body.
Therefore, buyers should request relevant documentation such as:
TDS
SDS
COA
Test reports
FDA-related documentation, where applicable
ISO 10993 test data, where applicable
Food-contact documentation, where applicable
The exact documentation should match the specific material grade, finished product, market, and intended application.
Common Silicone Rubber Applications
Different silicone rubber types are used in different industries.
- Gaskets
- Seals
- Connectors
- Cable protection
- Sensor components
- Tubing
- Valves
- Diaphragms
- Seals
- Medical device components
- Insulators
- Cable accessories
- Electronic seals
- Encapsulation
- Protective components
- Baking molds
- Kitchen utensils
- Seals
- Flexible components
- Wearable products
- Baby products
- Household products
- Personal-care products
FAQ
Q: Is LSR the same as silicone rubber?
A: No.
LSR is one specific type of silicone rubber. Other major categories include HTV/HCR and RTV silicone rubber.
Q: What is the difference between HTV and LSR?
A: The main difference is their physical form and processing method.
HTV/HCR is supplied as a solid, high-consistency silicone compound, while LSR is supplied as a liquid two-component system.
HTV is commonly processed by compression molding or extrusion, whereas LSR is commonly processed by liquid injection molding.
Q: Is HCR the same as HTV?
A: HCR means High Consistency Rubber, while HTV means High Temperature Vulcanizing.
The terms overlap substantially in commercial silicone terminology, but they describe slightly different aspects of the material: HCR emphasizes the material's high consistency, while HTV emphasizes its heat-curing process.
Q: Is RTV silicone the same as LSR?
A: No.
RTV refers to room-temperature vulcanizing silicone, while LSR refers to liquid silicone rubber.
Their formulations, curing systems and processing methods can be different.
Q: Which silicone rubber is best for injection molding?
A: There is no universal answer.
LSR is often selected for high-volume precision injection molding because it can be automatically metered, mixed and injected into heated molds.
HTV/HCR can also be used in injection molding depending on the material and equipment.
The appropriate choice depends on product design, production volume, tooling, equipment and required properties.
Q: Is all silicone rubber food grade?
A: No.
Only specific formulations and grades are designed and tested for food-contact applications. The applicable regulatory requirements should be verified for the intended use and target market.
Q: Is all LSR medical grade?
A: No.
Only specific LSR grades are developed and appropriately tested for medical or healthcare applications.
FDA's biocompatibility framework emphasizes evaluating the actual medical device and its material contact characteristics rather than assuming that a material category alone establishes biocompatibility.