Silicone 3D DLP Printing: Why Material and Process Must Work Together

Silicone DLP 3D printing is not simply a matter of loading silicone into a conventional DLP printer. Silicone flows differently, cures differently, and requires a dedicated printing and post-processing approach. That creates two interconnected challenges: developing a light-curable silicone chemistry and building a production workflow capable of controlling its high viscosity, layer formation, cleaning, and post-curing. Standard DLP resins use fundamentally different chemistry, while most DLP printers are designed for low-viscosity materials that flow and level easily.

At Spectroplast, we developed our patented TrueSil chemistry together with the printing and post-processing workflow needed to use it reliably. This connected material-and-process system makes true silicone parts possible: From initial prototypes to production volumes, without injection tooling.

What Is DLP 3D Printing (And Why We Use It)

DLP (Digital Light Processing) printers cure an entire layer of liquid resin at once using a projected image, instead of tracing it point-by-point with a laser the way SLA does. That makes DLP fast, and it's also highly precise, capable of fine feature detail and a smooth, almost injection-molding-like surface finish. That combination of speed, detail, and surface quality is why DLP has become one of the most widely used technologies for functional prototypes and, increasingly, production parts.

There are two main DLP architectures, and the difference matters a lot once you introduce a highly viscous material like silicone:

Bottom-up DLP: the light engine sits below a resin vat with a transparent window. The build platform starts near the window and lifts upward after each exposure. Every cured layer must "peel" away from that window before the next layer can form. Peel force scales with the cross-sectional area of the layer, so larger parts need more separation force, increasing the risk of distortion or print failure. This peel-and-refill cycle also depends on low-viscosity resin, since fresh material must flow quickly into the thin gap between the film and the part before the next exposure something a highly viscous material like silicone can't do.

Top-down DLP: the light engine sits above the vat and cures resin at the open surface. The build platform lowers into the vat instead of lifting out of it, and a recoating system, often a blade, spreads a fresh, defined layer of resin over the part before the next exposure. Because there's no window to peel from, this architecture avoids separation forces entirely.

Most commercial DLP resins are formulated and tuned for one of these two setups, almost always around low-viscosity acrylate chemistry. That assumption that the resin will flow easily and level itself is where silicone starts to break the mold, literally and figuratively.

Why the Standard DLP Resin Approach Doesn't Work for Silicone

DLP and SLA materials are photosensitive resins, typically formulated from three main components: monomers, oligomers, and photoinitiators. Under UV or visible light, the photoinitiator generates reactive species, free radicals, for example, that drive polymerisation and cross-linking of the monomers and oligomers into a solid network. Most photopolymer resins used in DLP and SLA are based on low-viscosity (meth)acrylate systems with relatively short molecular chains. When photocured, these systems can rapidly form a tightly cross-linked network. That can yield excellent print resolution and fast cure, but often at the expense of toughness. Over the past decades, polymer additive manufacturing has pushed this chemistry past its early limitations, tuning acrylates and methacrylates, and introducing new chemistries, to deliver more resilient, elastomeric performance. Silicone sits inside that same evolution, but represents an advancement step.

Conventional silicones, however, do not follow the AM-friendly free-radical photopolymer pathway, so making them printable typically requires chemical modification from the ground up. But even if you solve the chemistry problem, a second one is waiting: high-performance silicone is highly viscous, behaving closer to a thick paste than a free-flowing resin. Standard DLP recoating systems, vats, and exposure strategies are all designed around low-viscosity liquids that self-level in seconds. Push a high-viscosity silicone formulation through that same hardware and process, and you get uneven layers, poor leveling, trapped air, and inconsistent parts, or you end up adding a lot of waiting time per layer just to let the silicone spread evenly.

This is why true silicone has been so hard to bring to DLP: you need a chemistry breakthrough and a hardware/process breakthrough, together. Solve only the chemistry, and you still can't print it reliably. Solve only the process, and you still don't have a real silicone part in your hand.

TrueSil: True Silicone, Not a "Silicone-Like" Resin

TrueSil, together with a workflow designed around it, is Spectroplast's answer to both problems.

The chemistry side: TrueSil is our patented photo-silicone platform, a genuine silicone chemistry engineered specifically for light-based curing. It delivers real silicone performance: strong tear resistance, high elongation at break, low compression set, and full biocompatibility for skin-contact and medical-use applications. We offer TrueSil in five grades: A20, A35, A50, A60 translucent-white, and A60 Black, reaching up to 1000% elongation and over 15 N/mm tear strength. This is the part of the puzzle that makes the material true silicone in the first place.

The process side: solving the chemistry doesn't automatically make a material printable. TrueSil formulations are highly viscous, reaching up to 300,000 mPa·s, so we developed a dedicated printer architecture and post-processing workflow to accommodate this. Our printers use a top-down DLP architecture fitted with a recoater blade, which spreads each new layer to a precisely defined thickness across the build area regardless of how viscous the material is. Combined with a tailored exposure strategy and a post-processing workflow built around silicone's specific curing and cleaning needs, this gives us the repeatable process control required to print elastomeric silicone layer after layer, consistently, at production quality.

In short: TrueSil isn't a flexible resin engineered to feel like silicone. It's true silicone, made printable because we solved the material and the machine as one connected system, rather than treating either as an afterthought.

Why This Matters for Your Application

If you're developing a medical device, a soft robotics component, or a precision seal, the difference between "silicone-like" and true silicone tends to show up exactly when it matters most: Under mechanical stress, after sterilization, or over months of real-world use. TrueSil gives you production-grade silicone properties from the very first part you print, not just a part that looks and feels like one.

That also changes your path to production. Instead of validating a design in a compromise material and then re-validating it again in injection-molded silicone, you can validate directly in the material you'll actually ship. Small and mid-size production runs become fast and cost-effective compared to traditional silicone injection molding: no $10K–50K+ tooling investment, no 8–16 week lead time, and no compromise on material performance. You can iterate on hardness or geometry between runs instead of cutting a new tool, and scale confidently once the design is locked in.

It also keeps you flexible during the part of the process where changes are most likely: development and testing. If you commit to a mold and a few production runs later realize the part needs to change, you're looking at additional lead time and a lot of sunk cost in a tool that no longer fits. So even when the per-part cost of injection molding looks cheaper at first glance, that limited flexibility can end up costing you more once you factor in the risk of design changes during development and testing.

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FAQ: Silicone and DLP 3D Printing

What's the difference between a flexible resin and true silicone?

A flexible resin is a photopolymer engineered to feel soft; most are urethane- or acrylate-based, not silicone, and they don't replicate silicone's chemistry, durability, or long-term elastomeric behavior. True silicone is a siloxane-based elastomer that requires a dedicated silicone chemistry and a process engineered specifically to print it.

Why can't standard DLP printers just print silicone?

Even with a printable silicone chemistry, silicone's high viscosity causes uneven layers and poor leveling on hardware designed for low-viscosity acrylate resins. Printing silicone reliably requires an architecture such as top-down DLP with a recoater and a post-processing workflow built around that viscosity from the start.

Is Spectroplast's DLP silicone production-ready?

Yes. TrueSil is production-ready today. We've already printed over 120,000 parts, and several of our customers have used TrueSil parts to receive FDA clearance for clinical trials. With our Express option, parts can be ready for shipment within 5 days.

Is TrueSil silicone compatible with standard DLP printers?

Because our current TrueSil formulations are highly viscous, they currently benefit most from a top-down DLP architecture for robust, repeatable processing. For prototyping applications, formulation development is ongoing to also offer true silicone material running on bottom-up DLP printers.