April 17, 2017

Optical Liquid Silicone Rubber: A New Fixture in Molding

By Protolabs
optical LSR part

We offer many manufacturing processes and materials for prototype and production parts. But one process has a material that separates itself from the rest, optical liquid silicone rubber (OLSR). OLSR is an advanced material that has many properties that make it a preferred material choice over polycarbonate (PC) and acrylic (PMMA) for lighting and optical parts. Here are a few of the benefits that OLSR offers:

Light Transmission

Light transmission is lost as light passes through a material. PC, PMMA, and even glass will have light loss with glass retaining up to 95 percent, PMMA around 93 percent, and PC between 88 to 90 percent. When your product requires a clear PC or PMMA part, you can improve on light transmission using OLSR, which retains up to 94 percent light transmission. How about the refractive index? OLSR has a low refractive index of 1.42 when compared to PC and PMMA, which are at 1.58 and 1.49 respectively.

  Silicone PC PMMA Glass
Light Transmission 94% 88-90% 93%


Refractive Index 1.42 1.58 1.49


UV Resistance High Low Medium


Chemical Resistance High Medium Low


Temperature >150°C 120°C 90°C


Yellowing No Yes Yes


Micro Detail Yes No No


Thick Part Yes >1 in. No  >PC


Minimum Part Thickness <0.020 in. 0.040 in 0.040 in


Still another advantage is the non-yellowing factor. Thermoplastics without additives are not UV resistant, which means the parts could yellow and degrade over long exposures to lights and sunlight. OLSR is non-yellowing so it’s great for outdoor fixtures exposed to harsh environments. Heat and Chemical Resistance Because OLSR is durable under temperatures that may be close to exceeding 300°F (150°C), and able to withstand many chemicals that may break down thermoplastics, you can use OLSR in high-power light fixtures, solar power, outdoor fixtures, LED lighting, cleaning fixtures, and many other environments where PC and PMMA may fail.

optical LSR lighting component
Injection Molding Resilience

In plastic design, thick and thin parts are not easily achieved without sacrifice. That doesn’t necessarily ring true with OLSR design. You can achieve thick and thin geometries that oftentimes can be as thin as 0.010 in. (0.25mm) and as thick as 2 in. (50mm), all within the same part geometry because you don’t have issues with material flow, sink, or voids.

OLSR is extremely resilient against the molding issue that frequently create problems with thermoplastics, including the ability to create micro details. You also can design in negative draft angles without the need for expensive tooling that normally requires lifters, collapsible cores, and side-actions.

When to Use

As you learn about the benefits of OLSR, the applications where you can use OLSR are numerous:

  • Reducing part count in your design with built-in gaskets
  • Lenses of all types
  • Lightpipes or guides
  • Marine and wet environments
  • Outdoor and indoor light fixtures
  • Low- and high-heat environments
  • High impact parts

To learn more about optical liquid silicone molding and other molding, machining, and 3D printing services at Protolabs, visit protolabs.com. You can also contact us at  [email protected] or 877.479.7541 to speak with one of our knowledgeable applications engineers.