How to Choose the Right LSR Grade for Medical, Automotive and Consumer Products

Liquid silicone rubber is available in many formulations that may appear similar but perform very differently in production and final use.

Two LSR grades with the same Shore A hardness can differ in:

• Tear strength
• Удлинение
• Остаточная деформация при сжатии
• Прозрачность
• Self-lubrication
• Heat-aging resistance
• Химическая стойкость
• Adhesion to plastics or metals
• Biological-support documentation
• Food-contact status
• Cure speed and molding behavior

For this reason, selecting an LSR grade should never be based only on hardness, color or price.

The correct material must satisfy three groups of requirements:

1. Product performance: How must the finished component behave?
2. Application compliance: What contact, safety and documentation requirements apply?
3. Manufacturing compatibility: Can the grade be molded consistently in the intended geometry and production process?

LSR is generally supplied as a two-component material that is metered, mixed and rapidly heat-cured during injection molding. Its processing characteristics make it suitable for automated production, thin sections, complex geometries and high-volume manufacturing. Commercial LSR portfolios cover automotive, healthcare, electrical, food-contact and general consumer applications.

This guide explains how to select an appropriate LSR grade for medical, automotive and consumer products.

Begin with the Application, Not the Material Datasheet

A material datasheet becomes useful only after the application requirements have been defined.

Before comparing LSR grades, document:

• Intended product function
• Type of user contact
• Продолжительность контакта
• Operating-temperature range
• Exposure to water, oils, fuels or cleaning agents
• Необходимая гибкость
• Required sealing pressure
• Expected product life
• Number of compression or actuation cycles
• Sterilization or cleaning process
• Transparency and color requirements
• Plastic, metal or cable inserts
• Production volume
• Целевой рынок
• Required compliance documents

A medical valve, automotive connector seal and consumer drinking accessory may all be made by LSR injection molding, but they should not automatically use the same formulation.

The selected grade must match the actual risk and performance profile of the component.

Understand the Main LSR Selection Criteria

Shore A Hardness

Hardness affects how easily an LSR component deforms under pressure.

Softer grades can provide:

• Lower compression force
• Better conformity to uneven surfaces
• Greater cushioning
• A soft-touch feel
• Easier deformation in valves and diaphragms

However, very soft materials may also have:

• Lower dimensional stability
• Greater risk of seal rolling
• More difficult automated handling
• Increased dust attraction
• Greater demolding deformation
• Lower resistance to extrusion

Harder grades may provide:

• More stable dimensions
• Easier handling
• Stronger support for thin features
• Greater resistance to displacement
• A firmer tactile response

They may also require higher assembly or actuation force.

Hardness should therefore be selected together with wall thickness, seal geometry and expected compression.

Tensile Strength and Elongation

Tensile strength indicates how much pulling stress the cured material can withstand, while elongation describes how far it can stretch before breaking.

These properties are important for:

• Thin membranes
• Stretchable components
• Wearable straps
• Valve elements
• Demolding of undercut parts
• Repeatedly flexed products
• Components assembled over rigid features

High elongation is useful, but it should not be considered alone. A highly extensible material may still tear easily at a sharp corner or molded notch.

Tear Strength

Tear strength is particularly important when a component includes:

• Thin sealing lips
• Slits
• Openings
• Snap-over assembly features
• Narrow wall sections
• Deep undercuts
• Repeated bending points

LSR parts often fail from a small cut or edge defect rather than uniform tensile loading.

A product that must be stretched during installation should be designed with rounded transitions and sufficient tear resistance.

Compression Set

Compression set measures how much permanent deformation remains after an elastomer has been compressed for a defined time and temperature.

It is especially important for:

• Automotive connector seals
• Perimeter gaskets
• Medical seals
• Long-term housing seals
• Уплотнительные кольца
• Cable-entry components

Low compression set helps a seal retain contact pressure during prolonged use.

Automotive-specific LSR grades may be formulated for low compression set, self-lubrication and resistance to thermal aging. For example, published supplier portfolios identify specialized materials for cable seals, mat seals, grommets and connector gaskets rather than treating general-purpose LSR as interchangeable with automotive sealing grades.

Modulus

Modulus describes the resistance of the material to deformation.

Two grades with the same Shore hardness may have different force-deflection behavior.

Modulus affects:

• Valve-opening pressure
• Button-actuation force
• Seal compression
• Diaphragm movement
• Assembly force
• Product feel

For functional parts, force testing on the actual geometry is often more useful than relying only on Shore hardness.

Прозрачность

Optically clear or translucent LSR may be required for:

• Medical fluid-path components
• Diagnostic products
• Товары для детей
• Lighting parts
• Optical interfaces
• Consumer products where cleanliness must be visible

Transparency can be influenced by:

• Состав материала
• Pigments
• Mold finish
• Толщина стенки
• Curing conditions
• Post-curing
• Contamination
• Sterilization or aging

A “clear” grade should be evaluated using the intended part thickness and surface finish.

Viscosity and Flow

Material viscosity affects mold filling.

Lower-viscosity LSR may be advantageous for:

• Thin walls
• Long flow paths
• Small sealing ribs
• Microfeatures
• Multi-cavity molds

However, highly fluid LSR can also increase the risk of flash at parting lines and around inserts.

The correct grade must be matched with:

• Gate size
• Runner system
• Cavity layout
• Venting
• Injection pressure
• Mold shutoff accuracy

Cure Speed

Fast-curing grades can shorten cycle time and improve production efficiency.

However, very rapid curing may reduce the available filling time for:

• Large components
• Long flow paths
• Multi-material parts
• Complex insert-molding projects

A material that cures quickly in a simple test mold may behave differently in a large production tool.

Post-Curing Requirements

Some applications or material grades may require post-curing to stabilize properties or reduce certain volatile residues.

Post-curing can affect:

• Размеры
• Твёрдость
• Цвет
• Остаточная деформация при сжатии
• Volatile content
• Production cost
• Delivery time

The need for post-curing should be established before the quotation because it adds equipment, energy, handling and inspection requirements.

Choosing LSR for Medical Components

Medical LSR selection begins with the intended device use and the nature and duration of patient contact.

FDA’s biological-evaluation framework categorizes contact duration as limited, prolonged or long-term and considers the nature of body contact when identifying relevant biological endpoints. The biological suitability of silicone ultimately has to be assessed for its intended use, and data from the finished device are generally more relevant than data from uncured raw material alone.

Define the Contact Type

Determine whether the finished product contacts:

• Intact skin
• Mucosal membranes
• Compromised surfaces
• Tissue
• Blood
• A fluid path that indirectly contacts the patient
• No patient-contact area

A medical equipment handle touching intact skin is not evaluated in the same way as an implanted component or fluid-delivery valve.

Review Available Biological-Support Information

A candidate medical LSR grade may be supported by:

• Biocompatibility test information
• Chemical-characterization information
• Идентификация материала
• Отслеживание партий
• Processing recommendations
• Supplier change-control policies

Selected commercial LSR grades are marketed for healthcare applications such as valves, IV components, sealing elements, respiratory products and other precision medical components. However, the finished-device manufacturer remains responsible for determining whether the complete product is suitable for its intended use.

The review should confirm:

• The exact grade tested
• Whether the same pigment was included
• The curing and post-curing conditions
• Whether testing represents the final component
• Whether the data remain current
• Whether additional device-specific evaluation is required

Evaluate Sterilization Compatibility

Medical components may be exposed to:

• Этиленоксид
• Steam
• Гамма-излучение
• Электронно-лучевое излучение
• X-ray processing
• Испаренная перекись водорода
• Repeated disinfection

Sterilization can change:

• Цвет
• Прозрачность
• Твёрдость
• Удлинение
• Tear strength
• Остаточная деформация при сжатии
• Состояние поверхности
• Bond strength
• Extractable substances

Testing should use the intended sterilization process and the maximum expected number of cycles.

Consider Cleanliness and Manufacturing Controls

Medical products may require controls for:

• Cross-contamination
• Прослеживаемость материалов
• Чистота пресс-формы
• Post-curing
• Particle levels
• Handling
• Washing
• Упаковка
• Производственные отчеты
• Material changes

Not every medical-related silicone part requires the same production environment, but the factory controls should be appropriate for the identified risk.

Select Mechanical Properties for the Function

Medical applications may prioritize different properties:

Medical component	Important LSR characteristics
Valve or diaphragm	Controlled modulus, fatigue resistance, consistent dimensions
Respiratory mask seal	Softness, tear resistance, skin comfort, low compression set
Connector seal	Dimensional stability, sealing performance, traceability
Облицовка медицинских кабелей	Adhesion, flexibility, strain relief and tear resistance
Transparent fluid component	Clarity, cleanliness and representative biological evaluation
Wearable skin-contact part	Comfort, cleaning resistance and pigmentation control

“Medical grade” should not replace a detailed mechanical specification.

Choosing LSR for Automotive Components

Automotive LSR parts may be exposed to long-term heat, thermal cycling, vibration, humidity, oils, fuels and continuous compression.

К типичным областям применения относятся:

• Уплотнения разъемов
• Wire seals
• Mat seals
• Perimeter gaskets
• Sensor seals
• Cable-entry components
• Battery-system seals
• Plastic-and-LSR overmolded housings

Supplier product portfolios include automotive-specific LSR grades for connector seals, radial seals, weather-pack seals, grommets and wire-harness components, including self-lubricating and low-compression-set formulations.

Prioritize Heat-Aging Performance

Do not select an automotive grade using only its short-term maximum temperature.

Request information about:

• Continuous-use temperature
• Heat aging
• Property change after aging
• Compression set at elevated temperature
• Performance after thermal cycling
• Compatibility with adjacent thermoplastics

A seal may remain visually intact but lose sufficient recovery force to prevent moisture ingress.

Define Fluid Exposure

Standard dimethyl LSR may be suitable for many electrical and environmental sealing applications, but it is not automatically suitable for continuous exposure to every fuel, oil or solvent.

For aggressive hydrocarbon exposure, fluoro-LSR may be considered. Commercial F-LSR materials are designed to combine silicone-like temperature flexibility with improved resistance to non-polar fuels, oils and solvents.

Material testing should use the actual:

• Fluid
• Concentration
• Температура
• Exposure duration
• Mechanical condition

Evaluate Self-Lubricating Grades

Automotive connector seals can generate high friction when wires or terminals are inserted.

A self-lubricating grade may help reduce:

• Insertion force
• Seal tearing
• Seal displacement
• Assembly variation

Published automotive grades include different internal oil levels for connector and radial-sealing applications.

The complete connector should still be evaluated for:

• Lubricant migration
• Притяжение пыли
• Contact contamination
• Long-term consistency
• Storage effects

Consider Overmolding Adhesion

Automotive components frequently combine LSR with PBT, polyamide or other engineering thermoplastics.

Self-adhesive LSR can reduce the need for primer and separate assembly, but adhesion is substrate-specific. Dow describes selective-adhesion LSR grades for two-component molding with thermoplastics including PBT and polyamide.

The actual production plastic should be tested because adhesion can be affected by:

• Glass-fiber content
• Pigments
• Flame retardants
• Mold-release additives
• Moisture
• Surface contamination
• Insert temperature
• Storage time

Match Hardness to the Seal Geometry

A softer grade may reduce insertion or compression force, while a harder grade may improve dimensional stability.

The final selection should be verified through:

• Tolerance analysis
• Assembly-force testing
• Проверка герметичности
• Heat aging
• Thermal cycling
• Vibration testing
• Fluid exposure

Choosing LSR for Consumer Products

Consumer LSR applications can include:

• Baby feeding accessories
• Kitchenware
• Drinkware components
• Wearable products
• Personal-care products
• Sports accessories
• Защитные чехлы
• Appliance seals
• Buttons and keypads
• Household products

General-purpose LSR portfolios include grades designed for cooking products, gaskets, seals, sports equipment and other consumer goods.

Confirm the Contact Requirement

Consumer products may require different documentation depending on whether they contact:

• Food
• Drinking water
• Skin
• A child’s mouth
• Electronics
• Household chemicals
• No regulated contact area

A food-contact statement does not automatically establish suitability for a medical device. Similarly, a general consumer grade should not be presented as suitable for infant feeding without the relevant material and finished-product evaluation.

Balance Softness and Durability

Soft-touch consumer products are often designed using low-hardness LSR, but excessive softness may create:

• Poor dimensional stability
• Difficult assembly
• Прилипание к поверхности
• Притяжение пыли
• Weak thin sections
• Slow elastic recovery

For teethers, valves, buttons and wearable parts, the final selection should reflect both tactile preference and functional durability.

Evaluate Color and Appearance

Consumer products frequently require customized colors.

The pigment system should be reviewed for:

• Intended contact application
• Цветовая согласованность
• Light stability
• Heat resistance
• Migration or extraction requirements
• Effect on transparency
• Effect on curing

Strong colors may require more pigment, which can change appearance and, in some formulations, processing behavior.

Consider Odor and Volatile Requirements

Products used near food, the face or infant-care applications may require strict odor control.

Odor can be influenced by:

• Состав материала
• Curing
• Post-curing
• Storage
• Упаковка
• Уборка
• Contamination

The customer should evaluate finished packaged products rather than only newly molded samples.

Choose for the Actual User Experience

Consumer components may be evaluated through:

• Grip comfort
• Button force
• Текстура поверхности
• Flexibility
• Product weight
• Ease of cleaning
• Stain resistance
• Odor
• Притяжение пыли
• Visual appearance

A technically acceptable LSR grade can still fail commercially if the finished product feels sticky, attracts dust or is difficult to clean.

Standard, Self-Lubricating, Self-Bonding and Fluoro-LSR Grades

Different LSR families solve different problems.

General-Purpose LSR

Suitable for many basic molded products where special adhesion, fluid resistance or biological documentation is not required.

Typical uses include:

• Consumer goods
• Grommets
• Basic seals
• Sports products
• Household components

Medical-Support LSR

Selected for healthcare components requiring controlled formulation, traceability and relevant biological-support information.

The finished medical device still requires a risk-based evaluation.

Self-Lubricating LSR

Designed to develop a lower-friction surface.

Typical uses include:

• Уплотнения разъемов
• Sliding components
• Medical components requiring low surface friction
• Automated assembly applications

Momentive has described self-lubricating LSR formulations for healthcare applications requiring a high-slip surface.

Self-Bonding LSR

Designed to bond directly to selected plastic or metal substrates during molding.

Typical uses include:

• Plastic-LSR housings
• Overmolded medical connectors
• Automotive connector seals
• Soft-touch consumer assemblies

Compatibility must be verified using the exact substrate.

Fluoro-LSR

Selected where improved resistance to fuels, oils and non-polar solvents is required.

It may be useful in:

• Automotive fluid-exposure components
• Industrial seals
• Specialized electrical parts

F-LSR generally costs more than standard LSR, so it should be used where the exposure justifies the additional material cost.

Conductive LSR

Selected for:

• Antistatic components
• EMI shielding
• Conductive seals
• Electrical field control
• Flexible contacts

Electrical resistivity and test conditions must be specified separately from mechanical properties.

Overmolding Requirements

LSR can be molded onto plastic, metal, cable or electronic inserts.

Before selecting an overmolding grade, define:

• Insert material
• Insert geometry
• Bonding requirement
• Mechanical interlocks
• Insert temperature resistance
• Primer or surface-treatment needs
• Peel and pull requirements
• Fluid exposure
• Sterilization or aging conditions

LSR suppliers offer self-bonding grades formulated for selected thermoplastics and metals, but no grade should be assumed to adhere equally to every substrate.

A reliable overmolding evaluation should use:

• Production-grade inserts
• Actual pigments and fillers
• Production-intent mold temperature
• Representative cure time
• Finished-part aging
• Pull, peel or functional testing

Why Datasheet Values May Not Predict Finished-Part Performance

Technical data sheets are useful for comparing candidate materials, but the values are usually generated under defined laboratory conditions.

The finished component may behave differently because of:

• Толщина стенки
• Температура пресс-формы
• Время отверждения
• Gate location
• Flow orientation
• Weld lines
• Post-curing
• Pigments
• Demolding strain
• Insert interaction
• Sterilization
• Environmental aging

For example, a standard compression-set specimen does not reproduce every automotive gasket geometry. A biological test performed on a supplier specimen does not automatically represent a finished colored and sterilized medical component.

Use datasheet values to shortlist materials, then validate the final molded product.

Questions to Ask an LSR Material Supplier

Before approving a grade, request clear answers to the following questions:

1. What is the exact grade designation?
2. What is the recommended application?
3. Which hardness levels are available?
4. Is post-curing required?
5. What are the recommended molding conditions?
6. What biological-support data are available?
7. Is the grade suitable for the intended food-contact market?
8. How does it perform after heat aging?
9. What compression-set data are available?
10. Is it self-lubricating?
11. Is it self-bonding?
12. Which substrates have been evaluated?
13. Is it compatible with the intended sterilization method?
14. Is a fluoro-LSR version available?
15. What is the supplier’s change-notification policy?
16. What shelf life and storage conditions apply?
17. Can the material be pigmented?
18. Can production-lot traceability be provided?

Questions to Ask an LSR Molding Manufacturer

The molder should also be able to explain:

1. Whether the selected grade can fill the proposed geometry
2. Whether the mold requires vacuum assistance
3. Where gates and parting lines will be located
4. What flash limits can be maintained
5. Whether delicate features can be demolded without tearing
6. How inserts will be positioned
7. Whether primer or plasma treatment is required
8. How curing and post-curing are controlled
9. How critical dimensions will be inspected
10. How material and pigment batches are traced
11. Whether pilot production can be completed
12. Which functional tests can be supported

A material recommendation without a design-for-manufacturing review may overlook significant tooling or production risks.

A Practical LSR Grade Selection Process

Step 1: Define the Product Category

Determine whether the component is medical, automotive, food-contact, skin-contact, electrical or general consumer.

Step 2: Document the Service Environment

Define temperature, fluids, cleaning, sterilization, UV, humidity and expected life.

Step 3: Establish Mechanical Requirements

Specify hardness, compression, tensile strength, tear strength, elongation and fatigue requirements.

Step 4: Identify Special Functions

Confirm whether the project requires:

• Self-lubrication
• Self-bonding
• Optical clarity
• Conductivity
• Flame resistance
• Fuel resistance
• Low compression set
• Medical-support documentation

Step 5: Shortlist Candidate Grades

Compare supplier data and eliminate materials that do not meet the basic application requirements.

Step 6: Review Moldability

Evaluate viscosity, flow length, wall thickness, gates, venting, inserts and demolding.

Step 7: Produce Representative Samples

Use the intended:

• LSR grade
• Pigment
• Insert
• Cure process
• Post-curing process

Step 8: Test the Finished Component

Perform dimensional, mechanical, functional and contact-related evaluation.

Step 9: Complete Environmental Validation

Test after representative heat, sterilization, fluids, humidity, compression or repeated use.

Step 10: Freeze the Approved Material and Process

Control:

• Material manufacturer
• Exact grade
• Pigment formula
• Supplier
• Mixing ratio
• Cure parameters
• Post-curing
• Insert material
• Inspection method

Future substitutions should be reviewed and, where necessary, revalidated.

Quick Comparison by Application

Selection factor	Medical products	Automotive products	Consumer products
Primary concern	Biological risk and controlled manufacturing	Long-term sealing and environmental durability	Safety, function, appearance and user experience
Key documentation	Biological-support and traceability information	Heat-aging, compression and fluid-resistance data	Relevant food-, skin- or consumer-contact documents
Important mechanical properties	Tear strength, modulus, fatigue and cleanliness	Compression set, thermal stability and fluid resistance	Softness, durability, color and surface feel
Common special grades	Medical-support, transparent, self-lubricating or self-bonding	Low-compression-set, self-lubricating, self-bonding or F-LSR	General-purpose, food-contact, low-density or colored LSR
Typical validation	Finished-device biological and sterilization evaluation	Thermal cycling, leakage, vibration and fluid testing	Cleaning, odor, durability and user-function testing
Common error	Treating raw-material data as finished-device approval	Selecting by temperature or hardness alone	Prioritizing softness and color over durability

Common LSR Selection Mistakes

Choosing Only by Shore Hardness

Hardness does not describe tear strength, compression set, adhesion, lubrication or biological-support documentation.

Using a General-Purpose Grade for Every Application

A material suitable for a kitchen accessory may not be suitable for an automotive fuel seal or medical fluid-path component.

Treating Medical Grade as Finished-Device Approval

The final product, processing residues, pigments, cleaning and sterilization must be considered.

Assuming Standard LSR Resists Every Automotive Fluid

Fuel, oil or solvent exposure may require fluoro-LSR or another specialized elastomer.

Ignoring Post-Curing

Post-curing can affect cost, dimensions, odor and product performance.

Selecting Self-Bonding LSR Without Testing the Substrate

Adhesion depends on the exact plastic formulation and process.

Approving Material from a Flat Test Slab

The final component geometry may produce different tear, compression and optical performance.

Changing Pigments Without Review

Pigments can affect appearance, contact documentation and processing.

Selecting the Cheapest Grade

A less expensive material can create higher costs through longer cycle times, poor yields, flash, tearing or product failure.

Заключение

Choosing the correct LSR grade requires more than selecting a hardness and color.

The decision should consider:

• Product function
• Contact type
• Температура
• Chemical exposure
• Compression
• Tear and fatigue requirements
• Sterilization
• Прозрачность
• Surface friction
• Overmolding adhesion
• Regulatory-support information
• Moldability
• Production consistency

Medical products require a risk-based review of the complete finished device and its intended patient contact.

Automotive products typically prioritize low compression set, heat aging, fluid resistance, assembly performance and long-term sealing.

Consumer products require a balance of safety, tactile quality, durability, appearance, cleanliness and manufacturing cost.

The best LSR grade is not the material with the longest datasheet or the lowest unit price. It is the material that provides stable finished-part performance in the actual product, process and service environment.

Early cooperation between the product developer, material supplier, mold maker and LSR molding manufacturer can reduce material substitutions, mold modifications and validation failures before mass production begins.

Часто задаваемые вопросы

Can one LSR grade be used for medical, automotive and consumer products?

A grade may technically work in more than one application, but its documentation, environmental resistance and processing properties must be evaluated for each intended use.

Is a higher-hardness LSR more durable?

Not necessarily. Durability also depends on tear strength, elongation, geometry, aging and loading conditions.

Is medical-grade LSR automatically biocompatible?

No. Supplier data may support the biological evaluation, but the finished device and its intended contact conditions must still be assessed.

Which LSR is best for automotive connector seals?

Automotive connector applications often use low-compression-set and self-lubricating grades. The final choice depends on temperature, seal design, plastic compatibility and assembly force.

When should fluoro-LSR be used?

F-LSR should be considered where improved resistance to non-polar fuels, oils or solvents is required.

Can food-contact LSR be used for baby products?

It may be a suitable starting material, but the final product must also satisfy the relevant market, design and finished-product requirements.

What is self-bonding LSR?

Self-bonding LSR is formulated to adhere directly to selected plastic or metal substrates during molding, potentially eliminating a separate primer or assembly process.

Does self-bonding LSR adhere to every plastic?

No. Adhesion depends on the exact resin, additives, fillers, surface condition and molding process.

Is post-curing always required?

No. The requirement depends on the material grade, intended application and performance or contact requirements.

What information is needed for an LSR quotation?

Provide the 2D and 3D drawings, intended application, contact type, temperature, fluid exposure, hardness, color, insert material, annual quantity, compliance needs and required tests.