What Is Liquid Silicone Rubber (LSR)?
Silicone rubber, also known as food or medical-grade silicone is a popular material for consumer, healthcare, and industrial products because it’s skin-contact safe, durable, flexible, and soft to the touch. But not all material labeled “medical” grade meets that standard. To give our customers peace of mind, Casco Bay Molding uses full-traceability platinum cured medical grade silicone. We also manufacture all of our products per ISO:13485 standards and manufacture several FDA-registered parts. Quality is critical no matter the product you’re developing. That’s why we exclusively use medical grade silicone, otherwise known as LSR (liquid silicone rubber).
Wondering, what is liquid silicone rubber, exactly and how do you tell whether it’s of medical quality? Follow these insider tricks to manufacture the highest quality product — and abide by health regulations. Interested in developing a product from medical grade liquid silicone rubber? Casco Bay Molding is a global leader in silicone injection molding.
No matter your interest in silicone, here’s what you need to know about regulations, differentiating between types of material, and more.
What Is Silicone?
Silicone is an elastomer. This means that it’s a rubber-like material that can stretch, then regain its original shape. Technically, it’s a polymer and is best known for being:
Non-reactive
Flexible
Temperature-resistant
Water-resistant
There are many benefits to using material as durable, heat-tolerant, malleable, and biocompatible as this polymer. That’s why medical grade silicone is a favorite medical device manufacturer equipment and is commonly used in consumer products such as cooking utensils, face shields, and scuba gear.
Experts in Medical & Food Grade Silicone
We at Casco Bay Molding have experience designing, tooling, and high-volume manufacturing for a wide variety of medical, industrial, and consumer LSR parts.
Our engineering team has decades of product development and injection molding experience with this unique material, and we’d be pleased to help you develop your medical grade silicone application.
Have a product idea or medical part design in mind? Request a quote from our engineering team.
What Is Medical Grade Silicone?
A lot of companies use the term “medical grade silicone.” This generally means one of two things:
Medical-long term implantable material: This technical term describes a material that can stay in the body as part of an implantable device. Due to its purity, it’s generally too expensive for food-grade applications.
Medical grade: More technically referred to as medical-healthcare grade, class VI silicone tested for biocompatibility, this type is our material of choice for a wide range of products, including menstrual cups, baby bottle nipples, scuba mouthpieces, water pipes, and food and skin contact products.
Both medical-healthcare grade, Class VI, and medical-long term implantable are considered safe for food contact. Both grades are almost always defined as liquid silicone rubber (LSR), which is injection molded for clean, consistent parts.
ExerTies sleeve straps produced by Casco Bay Molding
Menstrual cup produced by Casco Bay Molding
What Is Silicone Made of?
You may have heard that it’s made from sand. That is technically true: Silicone is made from silica, the main constituent of sand. Silica is also known as silicon dioxide, which contains the elements silicon and oxygen.
What is the difference between silicon vs silicone? The former is a brittle chemical element commonly used in computer chips (hence Silicon Valley). The latter is a man-made material derived from silicon and oxygen.
Fun fact: Silicone rubber is not “naturally” derived from sand. It is a chemical process, meaning that these products cannot technically be “organic.”
8 Liquid Silicone Rubber Parts We Produce
We have over two decades of custom manufacturing experience and have our own product line as well. Here are a few examples of products we’ve produced or are currently manufacturing:
Silicone menstrual cups & discs
Catheter components
Sterilization tray components
Sleep apnea mask and ventilator valves
Dental instrument components
Face shield components
Frozen food suction cups
Medical gaskets
Injectible drug-device components
Scuba gear (mouthpieces, octopus necklaces, tank straps…)
Reusable sandwich bags
Overmolded faucet water spray face
Antibacterial doorknob covers
Cell phone cases
4 Types of Silicone Rubber Available
There are four major types of material commercially available. Here’s how to distinguish between them.
Liquid Silicone Rubber (LSR)
LSR is designed for injection molding and is almost always medical grade. This is delivered to us in either two sealed drums or 40 lb buckets. One drum/bucket has a catalyst, the other has the crosslinker.
The advantage of LSR is that it’s pumped directly from the drum/bucket into the molding machine with little to no possibility of modifying the material. The exception to this is if you add a colorant. For this reason, most medical parts are LSR.
High Consistency Rubber (HCR)
HCR is premixed and has a playdough-like texture. High Consistency Rubber starts with a “base stock” of silicone. Then, a catalyst and fillers/additives are added on a two-roll mill. After this, HCR is brought to the compression molding press to make parts or extruder to make tubes. HCR can be a platinum, peroxide, or tin cure system, see below for more info on cure systems
HCR has the advantage of being able to mix in different additives or fillers to change its physical characteristics. This can also be a disadvantage if the additive and filler amounts and ingredients are not shared with the end-user. It is also tempting for manufacturers to use extra filler — filler is much cheaper than food safe silicone rubber — to make more parts with the same amount of silicone base material.
How Can You Check Whether Something is 100% medical grade silicone?
Many LSR products—even those with labeling that suggests otherwise—contain filler due to high material costs. To check whether a product has filler, stretch it using your fingers. If the material turns white, it contains a filler.
Fluorosilicone Silicone Rubber (FSR)
Flame resistant, brake fluid resistant material is mostly used in the auto industry. Its benefits are resistance to compression, stability, and resistance to solvents. Casco Bay Molding does not use this type of material.
Room Temperature Vulcanize Silicone (RTV)
RTV solidifies or vulcanizes at room temperature. It is typically used in prototype parts and silicone caulks fall into this category.
Silicone scuba diving mouthpiece produced by Casco Bay Molding
Menstrual cup produced by Casco Bay Molding
Is Silicone Supposed to Turn White When Stretched?
No. If it does, it contains fillers, which are a cheaper alternative to medical grade materials. HCR (High Consistency Rubber) is frequently loaded with filler that turns white when stretched. However, stiffer durometers (60, 70, and 80 durometer) have some amount of filler required to stiffen the material. Generally, this is still not noticeable when stretching LSR parts.
High Temp Silicone Curing
There are different ways to “cure” silicone rubber. Curing is a chemical process during which the material transitions from a liquid or gel to a solid. It typically occurs when the material is exposed to oxygen, though there are different ways to accelerate the process.
There are several different catalysts that a manufacturer can add. Liquid silicone rubber and HCR cure quickly when exposed to high heat (350F +/- 60F). At room temperature, it may take days for LSR or weeks for HCR to cure.
That isn’t ideal for most manufacturers or product lines. With that in mind, most use a curing system. The following are the three most common you’ll encounter.
Platinum Silicone
LSR is almost always platinum-catalyzed. However, properly molded platinum menstrual cups do not need to be post cured. Platinum cured LSR is generally medical grade silicone and what we use at Casco Bay Molding.
Peroxide
A good deal of HCR silicone is peroxide cured and used for extrusion, transfer, or compression molding. Peroxide cured HCR needs to be post-baked in order to remove the volatiles. This can be a time-consuming and expensive step.
If a company tries to cut costs by shortcutting the necessary post-bake step, volatiles can remain in the material. Peroxide cure systems are generally much less expensive than platinum systems but require a time-consuming post-bake.
Casco Bay Molding does not do extrusion or compression molding. Our expertise lies in medical grade silicone production and design, for which injection molding is most suitable.
Tin Condensation Cure Systems
The third type of curing system, tin condensation is not recommended for healthcare or medical applications. This is because the tin (Sn) remains in the compound after curing.
Is Silicone Plastic? Here’s How They Differ
Though silicone and plastic are sometimes placed in the same rubber category, it’s important though they have a number of distinct characteristics. Here are a few reasons why we prefer to work with liquid silicone rubber (LSR) over conventional plastics:
It lasts much longer than plastic. This makes it a more sustainable and higher-quality alternative.
Silicone is more biocompatible, meaning safe to use within the body or with food, in comparison to plastics. This is why sensitive products, such as baby bottle nipples and spatulas, are best made from it.
It does not create “microplastics,” one of the main environmental issues with plastic. These are small, sometimes microscopic pieces of plastic that may contaminate drinking water and affect ecosystems.
Heat resistance is another important characteristic. For example, molecules do not seep into the contents when exposed to heat.
And, like plastic, food grade silicone is extremely versatile from a manufacturing perspective. It can be molded into a variety of products big and small with our injection molding know-how.
For all these reasons, we believe it to be safer for a variety of sensitive applications in comparison to TPE or latex, two commonly cited plastic alternatives.
Your Questions about Silicone Rubber, Answered
As a manufacturer with over two decades of experience designing and producing medical-grade parts, we receive a lot of questions about our materials — and how to check material quality more broadly. An independent menstrual cup advocate asked us the following questions, which we decided to share here for everyone’s benefit.
To answer these questions, our president Andrew Powell discussed with three trusted silicone chemists. These chemists have decades of experience at several silicone manufacturers, including Momentive/GE, Wacker, Dow, and Blue Star.
Will All Silicone Rubber Turn White?
“That was a company’s [not Casco Bay Molding] reply when asked about their “Medical Grade Silicone” Menstrual Cup (made in China). One retail company said that it’s a flaw in the material due to high curing temperatures. Another said that it depends on which molding process is being used; compression molding or injection molding because the molding process changes the silicone structure.”
Silicone will not turn white when stretched unless it has additives used to reduce the cost of the material. Products manufactured at Casco Bay Molding will not turn white when stretched.
Vulcanization is a chemical process for natural rubber and man-made silicone. For both LSR and HCR the silicone processor should not try to mix in the extra filler. The compound should be used as received.
Is Vulcanized Compression Molding the Best?
We strongly believe that injection molding produces the highest quality parts. In the case of menstrual cups, we believe that they’re best produced with the smallest amount of unknown fillers, additives, and volatiles possible. This means platinum liquid silicone rubber. At Casco Bay Molding, we are strong advocates of full material traceability. We use the same procedures we use for medical device manufacturing.
Different part manufacturing methods (compression, transfer, injection) should be selected on a cost vs. performance basis. With peroxide cure HCR, extra filler should not be added and a proper post-bake should be conducted to remove all volatiles.
What Are Your Thoughts on Silicone and High Heat?
“Some companies suggest boiling a menstrual cup to sanitize it, while others suggest against it. I was under the impression that a silicone (food and/or medical grade) were created to withstand high temperatures for cooking and/or autoclaving.”
Real silicone has no issue with boiling water. We do not recommend a hot griddle or frying pan because the temperature is hard to monitor. Over 400F may cause discoloration but may not change the physical properties of the silicone. Silicone is flammable; It should never be exposed to an open flame.
We strongly recommend boiling your cups for sterilization, especially for women in nations where clean water is an issue. We also recommend boiling our menstrual cup case made from medical grade silicone.
What about Ash Testing?
“Another path my search took me, was through silicone sex toys. People have claimed that they test their toys by doing the “ash test”. This is the process of burning a good portion of the silicone item to see the outcome. They claim that a medical grade silicone will not continue to flame, will not melt, and will leave behind a pale gray ash and show no or minimal signs of damage.”
The ash test is a plastics laboratory test to check for volatiles in the plastic. There was a difference of opinion on silicone. For any skin contact or short term-internal body application, we recommend platinum cured medical grade class VI silicone.
Can Food Grade Silicone Rubber Be Clear?
“This came up on a sex toy site that “pure silicone will never be crystal clear and see-through.” I have always preferred a clear cup. It allows me to see if there are any flaws inside of the silicone. However, if it’s true that a “pure silicone” will never be clear, then I’ve been going about this all wrong.”
This is not necessarily true. Silicone rubber can have very high elasticity. Regarding clear material, with the advent of LED lights, there are a few optical grades on the market. With injection molding grade LSRs, mold surface finish has a lot to do with how translucent the menstrual cup appears. Many of our menstrual cups have a slight texture or frosted look. HCR generally is less translucent, especially if they use fillers.
Sex toys are relatively unregulated, which can translate to a lack of material certifications or traceability.
How Do You Check Medical Silicone Quality?
“I don’t doubt that some menstrual cups are made with lesser silicones/materials or “fluffed” with fillers to cut the cost of making them, but how are we to know? With menstrual cups becoming more popular all over the world, there have been a lot of cups being made that are questionable. Some are very thin or flimsy. Several are even too soft to seem usable.”
We could not agree more. This is why we are pleased to offer medical grade silicone rubber menstrual cups made in the United States. Our cup was primarily designed by our engineer Liz Thornton. We have spent years finding the right combination of part thicknesses, overall design, and proper material selection.
Our cups are platinum cured, FDA registered, have full material traceability, and manufactured from medical class VI liquid silicone rubber. They’re produced in our ISO 13485 Certified factory and we sell to foreign and domestic companies, stores, and NGOs. We also offer private label cups under the same manufacturing and quality conditions.
Our Medical Grade Silicone Rubber Processes
Casco Bay Molding continues to exceed our quality standards and shorten development time for our OEM and medical silicone and plastic parts. This includes the following services:
In-House Tooling and Precision Machine Shop: Not only are we able to create our molding machines to our exact specifications, but we are also able to adjust your silicone tooling in a timely fashion.
Experienced Engineering and Production Team: We are pleased to work with you to design your medical parts for cost and production efficiency whether you have an existing design or are starting from scratch.
Prototype and Short-Run Capabilities: Our short-run injection unit coupled with our core and cavity insert approach facilitates efficient short-run production.
High Volume Production: We cater to high volume production and have the ability to automate larger jobs.
Casco Bay Molding provides full-spectrum services from design to tooling to high volume production. We look forward to learning about your project whether it be silicone, plastic or overmolding of one on the other.