Speed, cost, and approximation to the final part design (including material properties and dimensions) are key criteria when selecting a fabrication method for making a silicone prototype. For silicone parts, there are actually more options than there are for thermoplastics, which makes the product development process for silicone products a little more challenging. Available processes for making silicone prototypes include: RTV (room temperature vulcanization) molding, liquid silicone rubber (LSR) molding, 3D printing, and high consistency rubber (HCR) molding. As we discuss these options, please keep in mind the vast majority of new silicone products are manufactured from LSR (liquid silicone rubber), injection molded in a durometer range of 30-70 Shore A.

 

A Review of 4 Methods

RTV Molding – Industrial RTV silicone formulations are widely available—some can even be found at the corner hardware store. Making parts out of these materials requires a mold, which can be made of almost any metal or plastic material. Although by definition RTVs will cure at ambient temperatures, albeit over hours, ovens are often used to accelerate the curing of the material.

Pros: The use of RTV is attractive because of the low capital equipment requirements and the availability of raw materials. RTVs can be a reasonable approximation to their LSR relatives. It is common that well-equipped R&D labs have the ability to manufacture tools from plastic and/or soft metal materials in-house. Once the mold is made, making parts is a simple fill-and-wait process.  

Cons: RTV molding is a slow process with cure times extending from 20 minutes to hours. Production rates and cost per piece are both largely determined by the processing time.

HCR – Transfer or gum stock injection molding is used to make parts out of HCR.  EIther process uses a process of forcing an HCR (“gum stock”) material into a heated cavity to cure and form a part. HCR is a natural fit for transfer molding since gum stock is much more viscous than LSR.  But a few companies also specialized in injection molding HCR gumstock, which allows for automated molding and lower costs.  

Pros: Simpler tools for transfer molding. Process development tends to be fairly straightforward..

Cons: Complex geometries may not be possible. Generally longer cycle times than LSR.

LSR – Production grade materials are injection molded, usually in soft metal tooling to reduce tooling costs and shorten lead times.  .

Pros: Tooling can be made relatively quickly and substantial quantities of prototypes can be produced quickly.. The resulting prototypes can be close approximations of production parts.

Cons: Can result in a higher cost per part for small runs of parts, since the initial tool cost isn’t be amortized over a large number of parts.

 

3D Silicone Printing

There are a variety of 3D printed materials available, but silicone is inherently more difficult to print because of its heat cured nature.  As a result, this technology lags many years behind thermoplastic 3D printing.

3D parts of silicone are generally a poor approximation of production parts.

 

Frequently Asked Questions

 

1)  What Types of Silicone Rapid Prototyping Services Does ProMed Offer?

ProMed offers a comprehensive suite of silicone rapid prototyping services to support various stages of product development, from early concept evaluation to final design validation. These services include RTV (Room Temperature Vulcanization) molding, HCR (High Consistency Rubber) transfer molding, and LSR (Liquid Silicone Rubber) injection molding. RTV molding is well-suited for quick-turn, low-volume prototypes and involves creating a mold from soft materials such as plastic or aluminum, allowing for cost-effective, small-batch part production. HCR transfer molding uses gum stock silicone and is ideal for functional testing when greater material fidelity is required. For high-fidelity prototypes that closely resemble production parts, ProMed uses LSR injection molding with soft aluminum tooling. This method is often employed for regulatory testing and clinical trials. Additionally, ProMed supports hybrid approaches, such as using 3D-printed molds for RTV or overmolding prototypes onto rigid substrates, offering clients the flexibility to move from prototype to production with minimal disruption.

 

2)  How Does ProMed Determine Which Prototyping Method is Best for My Project?

ProMed collaborates closely with each client to recommend the most appropriate prototyping method based on several critical factors, including timeline, budget, part geometry, and material performance requirements. If the goal is to quickly evaluate the form or basic fit of a component, RTV molding can be a valid choice due to its rapid turnaround and minimal tooling costs. 

For more advanced stages of development—such as design validation, regulatory submission, or clinical trial preparation—ProMed typically recommends molding prototypes. Using processes and tools that are closer analogs to production-grade materials and tooling, one can create prototypes that can be indistinguishable from final production parts. Molding of prototypes also allows for development of production processes and initial assessment of those processes’ capability and cost effectiveness.   

 

3)  What are the Typical Lead Times for ProMed’s Silicone Prototyping Services?

Lead times for ProMed’s prototyping services vary depending on the method selected and the complexity of the part. HCR transfer molding, which involves robust prototype tooling, generally requires ~2 weeks for tooling and an additional week to produce the first parts. LSR injection molding, which offers the highest fidelity to production, takes slightly longer—usually three weeks to complete tooling, with initial parts available within a week thereafter. These timelines reflect ProMed’s ability to rapidly iterate while maintaining a high standard of quality. For urgent projects, expedited services and parallel tooling development may also be possible.