What is Silicone Rubber?

The High-Temperature / Low-Temperature Rubber Material

Working Temperature Range:

High: 450°F / 232°C Low: -75°F / -59°C

What is Silicone? What is Silicone Rubber?

Technically Silicone is a synthetic elastomer composed of silicone (a polymer containing silicon, carbon, hydrogen, and oxygen). Silicone rubber is sometimes used interchangeably with just silicone, and this is done when silicone is used in an application where you could consider using other alternative rubber materials.

Its unique blend of properties makes it a great option for a very wide range of products. Silicone rubber can be found across several industries including automotive, household products, medical, aerospace, power generation and more. It is more expensive in comparison to other materials, but its excellent resistance to extreme temperatures often means it's the only or ideal choice for products exposed to high heat or freezing cold.

If Silicone rubber is the ideal material for your application, give Custom Rubber a call. Even if you aren’t certain, our team of experts can help guide you. Contact Custom Rubber Corp. for answers to your silicone rubber questions.

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Advantages of Silicone Rubber
There are several benefits to using silicone rubber. It has an excellent tactile feel and works great as a sealant. Other advantages include:

  • Excellent extreme temperature properties
  • Good compression set
  • Excellent tactile feel
  • Chemical Resistance
  • Weather Resistance

Disadvantages of Silicone Rubber
Silicone rubber has several disadvantages, including its higher-than-average price point and lower tensile strength. Other disadvantages include:
  • Poor abrasion resistance
  • Lower / fair tear resistance

Commonly Asked Questions About Silicone Rubber

The following questions regarding Silicone rubber applications, properties and uses are frequently asked by our customers. Custom Rubber Corp. is here to provide answers and assist in your decision making process.

Q: What are the common uses of silicones?

A: Common uses for silicone rubbers include:
  • Automotive gaskets & seals: Silicone works exceptionally well in high temperatures like those found in vehicle engines. More than 50% of the silicone used in the U.S. Is used by the automotive industry.
  • Medical equipment: In healthcare, silicones are used for fluid transfer, tubing, valves and medical devices.
  • Aerospace products: Because silicone stays flexible at both high and low temperatures, it's an ideal material for vehicles traveling in and out of Earth's atmosphere.
  • Power generations: Silicone can be conductive, depending on its own formulation. It also withstands high temperatures, making it great for electrical and power applications.

Silicone is also commonly used in many household products due to its excellent tactile field. Cases for electronics are often made of silicone because the material is fairly inert once molded, meaning it won’t easily change color or feel over time. Other household products made of silicone can include baby bottle nipples, cooking spoons and silicone baking trays.

Q: What are the different types of silicone rubber?

A: There are several types of silicone that vary in their formulations. Some of the most common are Flurosilicone, High Consistency Rubber Silicone (HCR) and Room Temperature Vulcanizing (RTV) silicone.
  • Flurosilicone: An expensive type of silicone with improved temperature resistance and chemical resistance
  • Liquid Silicone Rubber (LSR): A heartier elastomer with increased harness and tensile strength. It is often used to withstand high heat and pressure in molded rubber products. LSR has a very low viscosity, meaning it can be used in injection molding or made into rubber sheets.
  • High Consistency Rubber Silicone (HCR): HCR is another version of silicone with increased hardness and temperature resistance. In comparison to LSR, it has a very high viscosity, giviing it an almost gummy texture. It is better suited for compression molding, transfer molding and extrusion.
  • Room Temperature Vulcanizing Silicone (RTV): Used for sealing, bonding and coating applications, these one or two-part systems are formulated to cure upon hitting oxygen, much like a caulk. They are often used for sealing engine gaskets.

Q: What's the difference between HCR and LSR?
A: The main difference between HCR and LSR is that HCR is their viscosity. HCR has higher viscosity and a “gummier” texture, while LSR has a lower viscosity. Additionally, HCR is generally used for smaller production batches while LSR only makes sense in high volume production.

LSR is better suited for high volume because the molds are expensive and the material is 2-2.5 times more expensive than HCR silicone. Also, stopping and starting a machine running liquid silicone can be complicated and expensive. If you leave the two parts in the machine combined they cure up and you end up taking the whole machine apart, cleaning up and starting over.

Another key difference is that LSR comes in two parts prior to vulcanization, both of which are liquid. When you combine them, they react chemically and vulcanize (or cure) quickly. HCR comes in either one or two non-liquid parts that will never become liquid, even after vulcanization.

Using LSR silicone can be trickier than HCR silicone, but sometimes you don’t have a choice. The material you use will depend on the desired qualifications of your end product.

Q: Why is silicone rubber expensive?

A: Compared to other rubbers, silicone is fairly expensive. This is mainly due to the high costs associated with its creation. It takes several steps to move from sand to refined silica, and even more to formulate the right type of silicone rubber for your application.

Silicone rubber is not as widely used as less expensive rubbers either, meaning it has a smaller economy of scale. All of these factors mean silicone is going to cost you extra, but it’s worth it for some applications.

Q: Does silicone melt in the boiling water?

A: Silicone rubber is not going to melt in boiling water due to its extreme temperature resistance. The boiling point of water just isn't enough to melt silicone.

This makes sense when you consider one of the most common applications of silicone rubber is stirring spoons for cooking. You wouldn't want your sppon to melt while preparing your pasta.

Q: What is the melting point of silicone rubber?

A: Silicone rubber melts at 1,414 °C or 2,577 °F

Q: Is silicone BPA-free?

A: Silicone rubber does not contain BPA. BPA is a component that’s sometimes added to containers, and is often referenced when people think of chemicals being leached into their food. Because of silicone rubber’s largely inert quality, it’s a great choice for cooking products.

None of Custom Rubber’s products are ever formulated with BPA.

Q: What additives and fillers are commonly used in Silicone rubber?

A: Just like any other rubber or elastomer, silicone rubber must be exposed to a catalyst to properly cure. There are two primary catalysts that are commonly used to cure silicone.

Two Primary Catalysts for Curing HCR Silicone
  1. ​Peroxide
  2. Platinum

Q: What is silicone rubber made from?

A: Silicone is primarily made of silica, commonly known as the main element found in sand. Silica is mixed with other elements, primarily hydrogen, carbon and oxygen, to create silicone rubber.

Q: Is silicone rubber flexible?

A: Silicone rubber is a flexible material. Like all other rubbers and elastomers, different formulations and applications control for the amount of flexibility. If you need to create a stiffer type of silicone rubber, specific chemical formulations can be derived. 

Q: Why was silicone rubber Invented? Who invented silicone rubber?

A: Silicone rubber was not invented by one person. It was more of a team effort. The Romans were the first people to discover how to create glass tools made from sand (or silica). Then, in 1823, Jöns Jackob Berzelius isolated the element silica on its own. 

A host of other scientists, including J.F. Hyde, Frederich Stanley Kipping, R. Müller and E.G. Rochow discovered and named silicone as a material, eventually determining how to make it synthetically. In 1949, James Wright accidentally made Silly Putty while experimenting with silicones. 

In the latter half of the 20th century, silicone was used for space travel, Post-It Notes, microchips and even contact lenses. Today the material is ubiquitous, used widely in industries like the medical, automotive and household product spaces.
Q: Is silicone hypoallergenic?

A: Silicone rubber is very inert (meaning that it’s unlikely to interact with other materials). It’s very uncommon for someone to have an allergic reaction to handling silicone, but not impossible.

Q: How do you tell the difference between rubber and silicone rubber?

A: The most common way we tell silicone apart from other rubbers is its smell. Silicone doesn’t smell like much of anything while most other rubber materials have a stronger “rubbery” smell to them. All of this, of course, is nose dependent. But the average nose should be able to spot the difference. 

Q: How can you harden silicone rubber?

A: As with any rubber, the right formulation can harden silicone, increasing its place on the Durometer scale. But once it’s molded the hardness can’t be changed.

Q: Can you mix different silicones?

A: You can mix silicones, but there’s no need to. Each type of silicone has its own purpose and properties and does not need to be mixed with other silicones.

Is Silicone rubber right for your application? Contact the Custom Rubber Corp. team today.

How Does Silicone Compare:

Natural NR Excellent Good -60F to 220F Poor Poor
Butyl IIR Excellent Fair -75F to 250F Good Poor
Ethylene-Propylene EPDM Good Excellent -70F to 250F Excellent Poor
Nitrile NBR Good Good -30F to 250F Poor Excellent
Neoprene / Chloroprene CR Excellent Excellent -60F to 220F Good Fair
Silicone VMQ Good Fair -175F to 450F Excellent Fair

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