With over a decade of experience in additive manufacturing, Kevin drives the success of Stratasys Direct’s 3D printing services portfolio, shaping material strategies, optimizing product sales, and enhancing customer experience through e-commerce platforms. He has expertise in powder bed fusion technologies like SLS, SAF, and MJF, contributing to material development and process innovations in industries such as aerospace, automotive, and consumer goods. Kevin holds both a BS and an MSE in Mechanical Engineering from the University of Texas at Austin and is an active speaker at industry conferences like AMUG and RAPID + TCT.
In the world of 3D printing transparent materials, few things are as visually striking – or technically challenging – as achieving true optical clarity. Whether it’s for medical modeling, visual prototypes, or fluidics, the ability to print crystal-clear components matters.
Among the various 3D printing technologies, Stereolithography (SLA) stands out for its ability to produce parts with exceptional detail and surface finish, making it the go-to choice for creating clear, optically transparent components. But did you know that build orientation and post-processing can dramatically affect just how clear SLA resin really looks?
In this article, we will discuss how part orientation during printing can impact the final transparency, highlighting the differences in clarity between parts printed flat versus on edge. We’ll compare three popular transparent SLA materials – Watershed XC 11122, WaterClear Ultra 10122, and 9120 – and explore how the four distinct finishing techniques influence part transparency.
If you’re designing for optical performance or need a clear coat for SLA prints, this article will provide an overview to help you choose the best material and finishing approach for your needs.
Clarity starts long before a part comes off the printer. One of the most overlooked contributors to transparency is part features and build orientation. Because SLA parts are constructed layer by layer, the direction those layers are stacked can dramatically affect how light refracts once the part is complete. Without post-processing, most printed parts are best described as translucent rather than optically clear.
In as-printed parts, layer transitions can scatter light, particularly in thicker sections or on surfaces printed in the Z direction. Parts built flat may appear clearer on broad faces, while parts printed on edge can reveal more visible layer lines. These effects are subtle to the touch but noticeable to the eye—especially when transparency is the goal.
When designing parts, avoid small features with disjointed faces, focus on smooth transitions, and ensure the surfaces are large enough to post processing. Sharp corners can create a focus point for light and also are difficult to sand—leaving a foggy appearance. Even when external surfaces are smooth, internal features and abrupt thickness changes can introduce visible optical artifacts by scattering light within the part. Maintaining consistent wall thickness helps reduce internal refraction and improves the perceived clarity of translucent parts.
Post-processing can reduce or eliminate many of these visual artifacts, but orientation still plays an important role in determining how much finishing is required. Designing with clarity in mind from the start can streamline post-processing and improve the final appearance of clear SLA parts.
When designing parts, consider how build orientation will affect critical features. Surfaces that require supports will develop small artifacts where the part contacts the support structure. These artifacts are typically sanded away, but sanding introduces surface scratches that leave a slightly foggy appearance. To achieve the desired transparency, ensure critical surfaces are fully accessible for post‑processing. Ideally, these surfaces are external to the part, allowing them to be sanded and finished evenly. Optical clarity can then be restored by applying a clear top coat, which fills surface scratches and improves light transmission. Our engineers at Stratasys Direct can guide optimal orientation based on your clarity or support removal needs.
When transparency plays a critical role in part performance, choosing the right SLA resin is the essential first step—especially since not all clear resins deliver the same level of optical clarity or are designed for the same applications.
Both Somos™ Watershed XC 11122 and Somos™ WaterClear Ultra 10122 are clear SLA resins designed to offer high transparency, they differ in their optical clarity and are not interchangeable.
While Watershed XC 11122 is a transparent SLA material, it has a slight hue that can make parts have a blue color to them. This is a popular choice for SLA functional prototypes that don’t require perfect transparency. On the other hand, WaterClear Ultra 10122 is a clear SLA resin that performs exceptionally well when a glass-like finish is needed.
The newest addition to the SLA resin lineup, Somos™ 9120, is designed to bridge the gap between flexibility, toughness, and clarity. This material expands design possibilities for applications that demand both offers a semi- Translucent material and enhanced mechanical performance. This material is the least optically clear, but offers additional mechanical properties if a frosted finish is preferred.
Each of these resins serves a distinct purpose, and selecting the right one ensures that clarity, strength, and performance are balanced appropriately. Whether left as printed or taken to a high-gloss polish, WaterClear Ultra provides the most optical-grade 3D printing result of the three.
The standard finish refers to the part’s condition immediately after the printing process, with only the support artifacts removed and sanded flush with the part’s surface. This is the fastest and least expensive, most basic post-processing step, requiring minimal effort: just the removal of the support structures that are used to stabilize the part during the build. This is the ideal finish when assessing geometry or general form.
The frosted finish is ideal when you want a smooth, consistent surface without full transparency – often used to diffuse light or soften internal features.
This finish is ideal for projects that require moderate visual clarity, such as engineering models or functional prototypes. It is a cost‑effective option that improves transparency while sealing the surface and providing basic UV protection. Layer artifacts remain visible, but overall light transmission and surface durability are improved.
For projects requiring the highest clarity—like optical components, light guides, or display models—this is your go-to finish. Applying this clear coat also results in a sealed part, slowing the yellowing UV affects and ensure a water-tight function.
This finish is the most time-intensive post-processing option, designed to achieve a high-clarity 3D printed part. This coating fills micro-groves and smooths out any remaining texture, transforming the surface to a highly transparent part.
Whether you’re printing a transparent 3D printing resin part for a medical device, a visual prototype, or a light guide, pairing the right material, finishing technique, and the right 3D printing partner – Stratasys Direct -- will make your parts truly shine. See for yourself: Get a quote.
