LSR is widely used in industries such as manufacturing, healthcare, and electronics. If you are looking for the right LSR material for your product, it is essential to understand its key properties. The properties of LSR directly impact the quality and compliance of your product. This article will explain 6 key properties of LSR and help you select the right one for your product.
What Is Liquid Silicone Rubber (LSR)?
Liquid Silicone Rubber is a high-performance, high-purity liquid synthetic rubber material. It has a wide range of applications. It is a two-component (A and B) material that is pumped into the mold as a two-component liquid mixture and cures into a solid when heated. As a thermosetting elastomer, its durability and ease of fabrication make it commercially viable.
6 Key Liquid Silicone Rubber Material Properties
Mechanical Properties
LSR has a unique molecular chain structure (Si-O-Si), which is more flexible than carbon chains. This structure can retain its elasticity under bending and stretching. Also, it is resistant to tearing.
LSR uses platinum as a catalyst to form a three-dimensional network structure during the curing process. This structure is uniform and stable, which allows the material to quickly return to its original shape when pressure is released.
These properties of high elasticity and tear resistance play a significant role in improving product durability. This makes LSR particularly suitable for thin-walled products (such as O-rings and keypad membranes).
Thermal Properties
LSR maintains stable performance between -60°C and 200°C. Therefore, liquid silicone rubber products can be used in environments with alternating hot and cold temperatures.
In addition, LSR exhibits excellent thermal stability. For example, a liquid silicone rubber pad placed in an oven at 180°C for one hour will not deform.
Compared to traditional organic rubbers such as NR, SBR, and NBR, LSR provides superior resistance to aging. This is because its oxidation rate is slow. Furthermore, the siloxane backbone itself is inherently stable against UV radiation and ozone, which makes it less likely to crack or harden.
Therefore, if your products require long-term, stable performance—such as some automotive parts, electronic components, medical supplies, and so on—you may want to consider LSR.
Chemical Resistance
LSR has strong chemical stability and excellent water resistance. Its molecular structure is not prone to chemical reactions with water. Also, it has a low water absorption rate, so moisture will be difficult to penetrate the material’s surface and enter its interior. As a result, it performs exceptionally well in humid environments or those subject to repeated exposure to water.
LSR has limited resistance to oils and is suitable for applications involving light oil contamination. LSR remains stable during short-term contact with oils such as lubricating oil and silicone oil. However, if immersed in oil for long periods—especially gasoline, kerosene, or mineral oil—it is highly likely to swell, deform, and experience a corresponding decline in strength and performance.
Therefore, if your product will be exposed to harsh oil environments, you may instead opt for NBR or FKM, which offer better oil resistance.
Electrical Properties
LSR is an electrical insulating material with excellent performance. It features high insulation, low loss, and modifiability. Through material modification, it can be flexibly switched between insulating and conductive states to meet your specific requirements.
LSR has a volume resistivity ranging from 1×10¹⁴ to 1×10¹⁶ Ω·cm. The dielectric strength of LSR ranges from 15 to 26 kV/mm. These figures tell you that it effectively blocks current flow through the material and is resistant to breakdown under high-voltage currents, which offers excellent insulation and voltage resistance.
The dielectric constant of LSR remains stable between 2.7 and 3.5, and its dielectric loss tangent is extremely low (<0.01). This means that LSR generates minimal heat in an electric field, which makes it particularly suitable for high-frequency electronic devices.
If you require high-voltage power accessories, high-voltage components for new energy vehicles, electronic components, or similar products, LSR is an excellent choice.
Biocompatibility & Safety
LSR is non-toxic and odorless. It does not contain harmful substances such as organic plasticizers or phthalates. It does not react chemically with food when in contact with it. Therefore, it is used in food and maternal and infant products, such as baby pacifiers, spatulas, and baking molds.
In addition, food-grade LSR materials typically meet certification requirements set by the FDA, LFGB, and other regulatory bodies.
LSR is unlikely to cause allergic reactions when in contact with human tissues and bodily fluids. It also remains stable under sterilization conditions. Consequently, it is frequently used to manufacture medical supplies, such as breathing masks, catheters, and medical valves.
Medical-grade LSR materials must also comply with USP Class VI and ISO 10993 standards.
Moreover, it is important to note that food-grade and medical-grade LSR must not be used interchangeably, as food-grade safety standards do not meet medical-grade safety standards. Furthermore, medical-grade LSR costs 1.5 to 2 times more than food-grade LSR, which could easily result in cost overruns.
Transparency & Aesthetic Flexibility
The transparency of LSR can be adjusted to meet your requirements. Untreated LSR is typically translucent or milky white, and this level of transparency is suitable for applications such as O-rings and standard buttons.
High-transparency LSR can achieve a haze level below 1%, which makes it suitable for applications requiring high clarity, such as O-rings and tubing.
Optical-grade LSR can achieve a haze level below 0.5% and a light transmittance of 94%–98%, offering optical properties comparable to glass while being lighter than glass. It is suitable for manufacturing optical components such as lenses and AR/VR waveguides.
In addition, if you need custom-colored LSR, it can be produced in any shade by mixing it with color paste. LSR has excellent color-retention properties. Adding just about 2% color paste is sufficient to achieve your desired color.
If you’d like to add a brand logo or pattern to your product, laser technology can engrave intricate designs onto the silicone surface. This not only improves your brand’s recognition but also helps differentiate your product.
Common Applications Based on LSR Properties
Medical & Healthcare
LSR is durable, resistant to disinfection, soft, and highly precise. So you can see it is widely used in the medical field.
Respiratory & Anesthesia: Anesthesia masks, CPAP mask gaskets, resuscitation masks.
Infusion & Drainage: Catheters, infusion set components, insulin pump tubing, infusion bag stop valves.
Sealing & Protection: Sealing valves, dialysis machine seals, syringe plungers.
Implants: Artificial heart valve sealing rings, pacemaker lead insulation, LSR shells for cochlear implants, breast implant fillers.
Consumer Electronics
LSR is widely used in the electronics industry because of its waterproof and dustproof properties, resistance to aging, and excellent insulation performance.
Buttons & Keypads: Mobile phone/computer keyboards, remote control buttons.
Waterproof Sealing: Waterproof components for mobile phones, smartwatches, and tablets.
Insulation & Encapsulation: Connectors, cable sheathing, sensor encapsulation, moisture-proof encapsulation of electronic components.
Automotive Industry
Because LSR features resistance to high and low temperatures, chemical resistance, and durability, it has many applications in the automotive industry.
Powertrain Seals: Engine seals, valve cover gaskets, radiator gaskets.
Electronics & Sensors: Radar housing seals, encapsulation of electronic components.
Hoses & Mounts: Fuel/coolant hoses, engine mounts, HVAC cushion pads.
Lighting & Interior: LED diffusers/headlight seals, steering wheel/armrest overmolding.
Baby & Food-Grade Products
LSR is a food-grade, safe, non-toxic, and odorless material that can withstand high-temperature sterilization, which makes it suitable for use in products for babies as well as food-grade applications.
Baby Products: Baby bottles, bottle nipples, bottle seals, baby spoons, baby toothbrushes.
Kitchenware: Collapsible water bottles, baking molds, silicone spatulas, silicone bowls.
How to Choose the Right LSR Based on Properties?
Temperature
The typical operating temperature range for LSR is 60 to 200 °C.
Standard LSR (-50°C ~ 200°C): Suitable for most products and the most widely used. Examples include waterproof gaskets, buttons, seals, and tableware.
High-Temperature LSR: Stable in high-temperature environments. Such as automotive engine components and silicone parts for coffee machines.
Low-Temperature LSR: Suitable for cold conditions. Such as seals for cold chain equipment and components for industrial equipment used outdoors in winter.
Hardness (Shore A)
The hardness range of LSR usually is between 10° and 80° Shore A. Products with different levels of hardness are different in terms of feel and functionality.
Low hardness (10–30A): Extremely soft, easily deformable, and highly resilient. Suitable for baby pacifiers, breathing masks, shock-absorbing insoles, etc.
Medium hardness (40–60A): Firm and resilient. Commonly used for phone cases, medical device gaskets, etc.
High hardness (70A and above): Rigid and wear-resistant. Suitable for silicone buttons, connectors, industrial vibration-damping pads, etc.
Certifications
Certifications for LSR are generally categorized into industrial-grade, food-grade, and medical-grade. You should select the appropriate certification level based on the usage. Industrial-grade: Complies with RoHS and REACH. Typically used for automotive parts, industrial sealing components, buttons, etc.
Food-grade: Complies with FDA 21 CFR 177.2600 or LFGB. Suitable for baby pacifiers, baking molds, water bottle gaskets, etc.
Medical-grade: Complies with ISO 10993 and USP Class VI certification standards. Suitable for medical supplies such as respiratory masks and catheters.
FAQ
Is LSR Suitable for Manufacturing Complex Micro-components?
Yes. LSR has excellent flow properties and can fill fine structures, such as 0.1 mm holes. In addition, LSR has a low shrinkage rate after curing (about 1.5-3.5%), enabling high precision. It is suitable for manufacturing micro-injection pumps, biochips, optical components, etc.
Is LSR Suitable for Overmolding With Other Materials?
Yes. LSR can be overmolded with a variety of materials like PBT, PC, PA, and some metals. LSR overmolding technology may level up the performance of your products.
LSR vs TPE: Which Should I Select?
You should consider your application requirements first. If you focus on the performance of your product, you can choose LSR. If you prioritize product recyclability and have a limited budget, then choose TPE.
What Are the Main Defects of LSR Products?
The main defects include voids and scorching. If air is introduced during the mixing of LSR material, it can cause voids in the finished product; vacuum-assisted injection molding can help reduce this issue. When the temperature is higher than the standard or the material stays too long in the hot runner, it may result in scorching. Lowering the temperature or shortening the curing time can effectively prevent this problem.
What Is the Cost of LSR?
The cost of LSR is mostly composed of material costs, mold costs, and equipment investment. The material cost for LSR is approximately $12–20 per kilogram. Mold costs are typically 25–50% higher than those for standard plastic injection molds. LSR-specific injection molding machines are relatively expensive. Therefore, the cost of LSR is relatively high, which makes it suitable for high-volume, high-precision automated production.
Final Thoughts
Knowing the key properties of LSR can help you make the right choice for your product. If you are looking for an experienced LSR manufacturer, Legensilico can meet your needs. We can provide you with professional tips and customized services. Feel free to contact us for further information.
