The Marvel of Molding: Different Types of Plastic, Rubber and Silicone Molding and How They Can Fit Any Application

With Contributing Expertise From: simtec

The Marvel of Molding: Different Types of Plastic, Rubber and Silicone Molding and How They Can Fit Any Application

The possibilities with rubber, plastic and silicone molding unfold like an infinite universe, so it can be overwhelming to navigate the industry and all of its offerings as you search for exactly the right “thing.” It might be anything from a rubber o-ring or weather stripping to a tiny computer part or element used in aerospace, but it is usually needed to accomplish a business goal or to complete some sort of mission or project.

Wherever you look, you will find confirmation that plastic, rubber and silicone molding can be crafted to fit just about any need or application.

Some type of molding can literally be found everywhere, in objects ranging from household items and appliances to industrial parts and manufacturing lines. Rubber, plastic and silicone molding is in our cars, homes and everyday products.


Molding usually consists of some kind of rubber, plastic or silicone compound subjected to a process that allows it to take a number of different forms. Sometimes the molding contains a mix of two or all three of those elements because the possibilities are so endless. Molding is often associated with the goal to create a seal or barrier that gives a bit, such as to expand or contract and then regain its original shape. The objective might also be to create a diamond-hard part or something stationary that is extra durable, flexible or some other characteristic to fit a certain specification.

Molding elastomers typically starts with some kind of uncured rubber, utilizing heat in most vulcanization processes. This material created is called a “thermoset”, where two components are fused into one and cannot be brought back into their original states. Rubbers and elastomers are naturally occurring materials that become synthetic through the various processes and formula additives.

Silicone’s most basic raw-material element is quartz sand. Its abundance and easily altered chemical structure can be modified and processed in a number of ways, including in unison with various thermoplastics and metals. Silicone is especially appreciated for its ability to repel water and resist heat, and some formulas for silicone can be proprietary and/or patented.


What kind of molding you need depends upon your specifications for the part, component, project or idea at hand. The names of rubber, plastic and silicone molding generally follow the kind of process used to create them.

There are several commonly known techniques used, listed alphabetically here:

1. Blow Molding is about the same as glass-blowing in that a heated tube or other implement is inserted into the material and air is blown through to enlarge the rubber/plastic/silicone to fit the mold. Once cooled, the object is removed. This technique is generally used to produce a high volume of hollow, one-piece objects.


  • Creates a hollowed shape needed for some projects.

2. Compression Molding involves using high pressure to squeeze a pre-formed piece of rubber into a mold between two or more plates, depending on the part or product configuration. The pre-formed piece of rubber must weigh more than the finished part so that when pressure is applied, all the air is expelled from the mold.

The excess is cut away, while the shaped product progresses to be cured using heat and more pressure, a process called vulcanization. Typically, compression molding fits the budget when the needed quantity is low and the part cross-section is large.

Compression molding usually has a longer cure time than other methods, but is well-suited to materials that require high density or a high level of hardness. The automotive industry is one example of a market that uses compression molding often because it offers superior strength for parts.


  • Existing compression tooling makes for lower costs
  • Technique does not require a high quantity
  • Ideal for medium- and large-sized parts or components
  • Able to handle any type of rubber, no matter how challenging or unwieldy

3. Extrusion Molding is usually used for making something long and hollow, such as a pipe, straw or some kind of tube. Unlike other methods where material is injected into a specific cavity detail, extrusion places the material directly through a die to determine the form it takes. The resulting long tube is then cooled and can be cut for diverse usages, including drinking straws and feeder-line applications for a bar, restaurant or agriculture.


  • Creates a unique tube shape for a number of different applications.

The Marvel of Molding: Different Types of Plastic, Rubber and Silicone Molding and How They Can Fit Any Application

4. Injection Molding (Hot Runner) uses a screw nozzle that is continuously fed by a barrel using a pump. For thermoplastics, a hot runner system is utilized where material travels to pack the mold full via a gate/runner/sprue system, which is terminology for the material’s entry point and distribution. The newly formed parts are cooled in the mold and solidify before an ejector system releases them from the cavity detail.

Injection molding and its variations are the most efficient molding process and normally fit needs for high quantities of small- or medium-sized items. It caters to components that require a high degree of uniformity, complex inserts and small dimensional tolerances.

Since it can be so precise as well as free from human contact, it is often the first choice for medical applications. The question “what is injection molding used for?” can be answered with a long list of products across many industries besides medical, too, such as electronics or automotive. The applications of injection molding have grown vastly over time to include nearly all industries and a multitude of products, components, parts and objects people need for business and leisure.


  • Eliminates pre-forms completely
  • Cuts out any human-operator handling of the component
  • Unit costs are generally low
  • Short production process

5. Cold Runner Injection Molding uses a closed, thermoset mold, but the rubber is liquid silicone and it comes in two parts, one of which has a platinum catalyst. Both are considered high-viscosity liquids, and they somewhat resemble cold molasses. A mixing-metering pump combines them and delivers the liquid into the injection device to be shot into the mold chamber. Within the heated mold the platinum catalyst compels a rapid-cure process that saves money and time compared to traditional processes.

Liquid Silicone Injection Molding is the preferred choice of the medical industry since the whole production process involves a closed system with no human contact and chances of contamination can be reduced or eliminated. It is most suitable for making micro-components but can accommodate a number of object sizes.


  • Ideal for high-volume production
  • Can be colored to suit
  • Has a short cure time

The Marvel of Molding: Different Types of Plastic, Rubber and Silicone Molding and How They Can Fit Any Application

6. Rotational Molding is also called rotomolding and rotates the mold as it is coated from the inside to form the desired product. It is a relatively slow process compared to other molding types and is usually suited for the creation of a large, hollow object such as a tank for liquid or gas. The centrifugal force of the rotational motion ensures evenly coated walls and little waste.


  • Economical for certain applications
  • Viable for manufacturing

7. Transfer Molding incorporates a container above the mold where the rubber sits and gets pushed into the mold using a piston-powered (sometimes called a plunger) gate/runner/sprue system.

The piece is then cured using heat and pressure. Transfer molding, like injection molding, will usually cost less per unit than compression molding since the rubber does not enter the mold cavity until after it closes and quantities are more exact.


  • Requires fewer pre-forms since one fills many cavities
  • Enables tighter control on dimensional tolerances since excess material does not push or hold the mold open, which is preferred for micro-component production
  • Color can be added
  • Lead time is short due to ease of process and preparation

All projects done with each kind of rubber/silicone/plastic molding vary by nature, size, complexity, quantity, purity and many other factors. The resulting products can have an indentation, a lip or ridge, holes or notches, grooves and other kinds of cavities within the mold.

They can be crafted for extreme hardness or great pliability, usually to whatever a client’s specifications demand. The project might call for a small quantity of something large or a big amount of something tiny, and usually it can be accomplished within the universe of molding and all its possibilities.

Liquid Silicone Rubber (LSR)

Liquid Silicone Rubber fits a multitude of applications for different industries. It not only has existed since the 1970s, but it is also unique in its innate properties. Many sources familiar with the different types of molding agree that injection molding is the most efficient, effective and versatile. It is the cutting edge of rubber/silicone/plastic molding and continues to improve as research and development advance new and better polymers and formulas.

SIMTEC Silicone Parts remains an industry leader and expert exclusively focused on extraordinary solutions for Liquid Silicone Rubber (LSR) parts, LSR over-molded parts and LSR 2-Shot components. That specialization has enabled us to develop parts and components that are both environmentally conscious and versatile enough to fit a variety of specifications.

General-purpose Liquid Silicone Rubber is naturally free of additives such as plasticizers, ensuring a clean, pure product. For special applications such as high-heat or oil-contacting environments, additives and fillers are able to be utilized.

The LSR 2-Shot process enables one molding machine to hold two mold cavity details, and is sometimes referred to as multi-shot injection molding. Immediately after the thermoplastic substrate is molded, the tool will either transfer or rotate to allow LSR to be injected directly onto it, permanently fusing the different parts and materials into one component.


  • Odorless, tasteless
  • Hypoallergenic, inorganic backbone
  • Hygienic — resistant to mold and bacteria growth
  • Hydrophobic —  repels water
  • High biocompatibility
  • Fatigue and tear resistant
  • Low compression set
  • High elongation
  • High thermal stability
  • Ozone and UV resistant
  • Performs at extreme temperature ranges
  • Custom colors available for many visually pleasing possibilities
  • Electrically insulative and conductive grades available
  • UL component recognition
  • Range of hardness levels available
  • Excellent for outdoor applications

So what is LSR injection molding used for? It excels in many electrical applications due to its insulative / conductive options as well as medical tools and parts since they can be made without human contact. The applications are practically endless once you begin to consider that LSR resists fire as well, so it’s good for building and other construction applications. Additionally, LSR repels and resists water, so it is a popular choice for marine-oriented professions.

Automotive items might include o-rings, gaskets, grommets, seals and other such components. Around the house, LSR can be found in your shower head, cosmetic applicators, print rollers, baby items and the buttons on your remote controls, among many others. For the medical industry, the objects might include things that touch the skin, such as a respiratory mask, needle-free valves, syringe stoppers, plates, caps, connectors, diaphragms, pumps, pull rings, gaskets, and seals.

The Marvel of Molding: Different Types of Plastic, Rubber and Silicone Molding and How They Can Fit Any Application

What Kinds of Companies Utilize Rubber, Silicone and/or Plastic Molding?

Just like at home, it would be difficult to think of a place where there is not some kind of molded component. It serves nearly every industry in some capacity:

  • Aerospace
  • Agriculture
  • Architecture
  • Automotive
  • Consumer goods
  • Construction
  • Dental
  • Electrical
  • Electronics
  • Energy/power generation
  • Engineering
  • Entertainment
  • Food service
  • Grocers
  • Manufacturing
  • Medical
  • Military
  • Plumbing
  • Printing
  • Publishing
  • Retail
  • Toys/games

Expert Manufacturers Refine the Process

SIMTEC produces custom designed and manufactured high-quality LSR parts and LSR 2-Shot components. Our capabilities and products fit a broad array of needs in a variety of industries. Since 2002 we have gained significant expertise through the production of billions of parts and components. Our specialty from the start has been LSR, and we have served clients that range from high-volume, sterile medical tools to specialty items and everything in between.

It is also worth knowing that SIMTEC provides all customized design and work. There are no cookie-cutter components, but rather there are free quotes and design assistance as well as help with prototype development from start to finish. Creating a new product requires hard science as well as creativity to envision the solution.

We encourage and invite everyone to better understand the molding processes and to feel confident that whatever it is they need, SIMTEC will be happy to provide guidance. Contact us today to get started.

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