How Volumetric 3D Printing Works Without Layers

Volumetric 3D printing creates entire three-dimensional objects in one shot, bypassing the layer-by-layer buildup that defines most additive manufacturing. Instead of stacking thin slices of material on top of one another, volumetric methods solidify a shape all at once inside a volume of liquid resin using carefully orchestrated light. The result is dramatically faster print times, smoother surfaces, and access to geometries that layered processes struggle with. The technology is still young, but it has already demonstrated some striking capabilities, from printing functional optical lenses in two seconds to fabricating living-tissue constructs embedded with cells.

How Tomographic Volumetric Printing Works

The most widely studied form of volumetric 3D printing borrows its core idea from medical CT scanning, but runs the process in reverse. In a CT scan, X-ray projections from many angles are combined computationally to reconstruct a 3D image of your insides. In tomographic volumetric additive manufacturing (sometimes called computed axial lithography, or CAL), a computer calculates a set of 2D light patterns that, when projected from many angles into a rotating container of photosensitive resin, add up to deliver enough light energy to solidify only the desired 3D shape. The resin is a liquid that hardens when exposed to sufficient light, and everywhere else it stays liquid and can be drained away.

The foundational demonstration of this concept came in 2019, when researchers showed they could print complex objects by rotating a vial of photopolymer through a dynamically changing light field, completing an entire print through roughly one full revolution of the container.

1Science. Volumetric additive manufacturing via tomographic reconstruction

Because the object forms everywhere simultaneously rather than one slice at a time, the process sidesteps a number of headaches that plague conventional 3D printing. There are no visible layer lines, no need for support structures to hold overhanging features in place while they cure, and no mechanical forces from a build platform peeling away from each freshly printed layer. A geometry that would take hours on a standard resin printer can solidify in seconds to minutes.

Alternative Volumetric Approaches

Tomographic printing with a rotating vial is not the only way to achieve volumetric solidification. A family of techniques uses intersecting beams of different-colored light to trigger polymerization only where two beams overlap. One approach, called xolography, sends a thin sheet of one wavelength of light through a flowing resin while a second wavelength projects a patterned image perpendicular to it. Polymerization happens exclusively at the intersection, allowing the system to build up a 3D object as the resin flows past the intersection plane.

2Advanced Materials. Continuous Volumetric 3D Printing: Xolography in Flow

A related strategy uses one color of light to initiate curing and a second color to actively inhibit it. In one implementation, a blue light source provides the curing energy through dynamic masking while an ultraviolet light sheet at 355 nanometers creates a thin anti-polymerization layer that prevents the cured part from sticking to the optical window. This enables continuous printing rather than the stop-and-peel cycle typical of bottom-up resin printers.

33D Printing and Additive Manufacturing. Rapid Continuous 3D Printing via Orthogonal Dual-Color Photoinitiation and Photoinhibition

These dual-wavelength methods differ from the tomographic approach in an important way: instead of solidifying the whole volume at once, they sweep a solidification zone through the resin. They are still “volumetric” in the sense that no discrete layers are deposited, but the build process is sequential in one axis. The practical upshot is that dual-wavelength systems can, in principle, handle larger build volumes because they do not require the entire resin bath to be optically transparent from every angle simultaneously.

Improving Light Delivery with Holography

One bottleneck in tomographic printing has been how efficiently light is delivered into the resin. Early systems used digital projectors that work by selectively blocking light, meaning most of the projector’s output is thrown away as heat rather than used for curing. A newer generation of systems replaces this with holographic phase modulation, which redirects light rather than blocking it. The improvement is substantial: one group reported that holographic light engines improved projection efficiency by at least a factor of 20 compared to amplitude-based coding, while maintaining diffraction-limited resolution.

4Nature Communications. Holographic tomographic volumetric additive manufacturing

That efficiency gain matters for more than just energy savings. With more usable light reaching the resin, the system can cure thicker or more absorptive materials, print at higher speeds, and achieve finer features. Researchers have used holographic volumetric printing to fabricate objects across a wide range of scales, from structures just hundreds of micrometers across to centimeter-scale parts, and in materials ranging from standard acrylate resins to soft hydrogels loaded with living cells at concentrations of one million cells per milliliter.

5Light: Science & Applications. High-efficiency multi-scale holographic volumetric 3D printing with a phase light modulator

The Photochemistry That Makes It Possible

All of these volumetric methods depend on resins that exhibit a threshold behavior: they remain liquid until they absorb enough light, then rapidly solidify. Getting that threshold right is what separates a crisp print from a cloudy, half-cured mess. In the most common resin chemistry, based on acrylate monomers, dissolved oxygen acts as a natural gatekeeper. Oxygen reacts with the radicals generated by light exposure and neutralizes them before they can start building polymer chains. Only once the local oxygen is used up do the radicals survive long enough to kick off actual solidification.

6PubMed Central. Advancing Tomographic Volumetric Printing Via Oxygen Inhibition Control: Improved Accuracy and Large‐Volume Capability

This oxygen-mediated threshold is what allows a computed light dose to solidify resin at the intended geometry without curing the surrounding liquid that received glancing or scattered light. The concentration of photoinitiator (the light-sensitive compound that generates radicals) has to be kept low enough that light can penetrate deep into the resin, which means every radical counts. Additives that recycle spent radicals from oxygen-quenched byproducts offer a way to make the process more efficient without sacrificing the threshold behavior that keeps prints sharp.

An alternative chemistry gaining traction uses a process called RAFT polymerization. Conventional free-radical polymerization is highly exothermic, and at scale the heat buildup can exceed 60°C, triggering runaway reactions that warp or ruin the print. RAFT chemistry moderates the reaction by introducing agents that reversibly pause and restart growing polymer chains, spreading the energy release over time and improving control over the final material properties.

7Nature Communications. Enhanced volumetric additive manufacturing via Reversible Addition-Fragmentation Chain Transfer (RAFT) polymerization

Printing Optical Lenses in Seconds

One of the more visually impressive demonstrations of volumetric printing is the fabrication of miniature optical lenses. Conventional lens manufacturing involves grinding and polishing glass or molding plastic, processes that are well optimized for mass production but slow and expensive for custom or low-volume optics. Volumetric printing offers an alternative path: print a near-net-shape lens in seconds, then refine its surface with a post-processing step.

The key post-processing trick is something called meniscus equilibrium coating, where a thin film of additional resin flows over the printed lens surface under the influence of surface tension, naturally smoothing out any remaining roughness before being cured in place. Combined with iterative correction algorithms that compensate for systematic errors in the printing process, this approach has produced millimeter-scale spherical lenses printed in about two seconds with sub-nanometric surface roughness and profile errors under five micrometers.

8Advanced Optical Materials. Low‐Cost Volumetric 3D Printing of High‐Precision Miniature Lenses in Seconds

Pushing this further, researchers have printed a 2.5-millimeter-tall spherical lens with an outer diameter of 9 millimeters at a rate of roughly 31,000 cubic millimeters per hour, achieving a surface roughness of about 0.33 nanometers RMS. For context, that roughness is on the order of the size of a few atoms, which puts it in the same league as traditionally polished optical glass.

9International Journal of Extreme Manufacturing. Ultra-fast 3D printing of assembly—free complex optics with sub-nanometer surface quality at mesoscale

Because volumetric printing does not build lenses layer by layer, there is no “staircase effect” where stepped layers create visible ridges on curved surfaces. That inherent smoothness, combined with post-curing surface refinement, makes the technique particularly well suited for optics where even tiny surface imperfections scatter light and degrade image quality.

10Hybrid Advances. Recent advancements in 3D printing methods of optical glass fabrication: A technical perspective

Bioprinting with Living Cells

Speed matters enormously when you are printing with living cells suspended in the resin. In conventional bioprinting, cells sit in a precursor material for minutes to hours while the structure builds up layer by layer, exposed to UV light, mechanical stress, and temperature fluctuations that can damage or kill them. Volumetric bioprinting slashes that exposure time by forming the entire construct in seconds, which translates directly into healthier cells in the finished product.

An early landmark study used visible-light tomographic printing with gelatin-based hydrogels to produce cell-laden tissue constructs with viability above 85%.

11Advanced Materials. Volumetric Bioprinting of Complex Living‐Tissue Constructs within Seconds

That result opened the door to printing structures with internal channels and cavities that could serve as rudimentary vasculature or guide tissue growth after implantation.

The challenge intensifies as you pack in more cells. At densities above about 10 million cells per milliliter, the cells themselves scatter the projected light badly enough to blur the intended dose pattern, degrading print resolution and making it difficult to form fine features like vascular channels. Computational methods that pre-correct the light patterns to account for scattering, combined with strategies to match the refractive index of cells and hydrogel so they scatter less, have pushed the achievable printing density to around 41 million cells per milliliter.

12arXiv. Overcoming Scattering in High-Cell-Density Tomographic Volumetric Bioprinting Using Computational Light Optimization

Higher cell densities matter because living tissues in the body are packed with cells. Printing at biologically relevant concentrations, rather than dilute suspensions, gets the constructs closer to something that could function as a tissue graft or an organ-on-a-chip model for drug testing.

Multi-Material Printing and Overprinting

Most 3D printing technologies struggle with building objects that contain more than one material. The standard workaround is to print separate components and assemble them afterward, but that defeats much of the purpose of additive manufacturing. Volumetric printing has developed several creative solutions to this problem.

One is overprinting: because the resin is a transparent liquid and the solidification is driven by light, you can place a pre-existing object inside the vial before printing and solidify new material directly around it. The tomographic projections are computed to account for the insert’s presence, and the result is a single integrated part combining the insert and the newly printed polymer.

13PubMed Central. Volumetric additive manufacturing of complex geometries around complex inserts

This capability is useful for embedding electronics, sensors, or metal reinforcements inside printed polymer housings without adhesives or mechanical fasteners.

Another strategy combines tomographic printing with embedded extrusion. A secondary material is first deposited into the resin bath in defined shapes using an extrusion nozzle, and then the surrounding photopolymer is volumetrically cured around it. The result is a multi-material structure fabricated in a single print session.

14PubMed Central. Additive manufacturing of multi-material and hollow structures by Embedded Extrusion-Volumetric Printing

Researchers have also extended volumetric printing to materials beyond polymers. One group demonstrated the printing of silica-based glass by using resins filled with ceramic particles or phase-separating precursors. The objects are printed volumetrically in seconds, then converted into actual glass through conventional high-temperature heat treatment. The approach allowed them to fabricate filtration devices combining dense and porous glass with tunable compositions in a single 3D structure, something very difficult to achieve with traditional glass-forming methods.

15Advanced Materials Technologies. Multimaterial Volumetric Printing of Silica‐Based Glasses

Yet another multi-material approach leverages thiol-ene photoclick chemistry in combination with algorithmic design tools to fabricate complex heterogeneous shapes rapidly. Unlike standard free-radical acrylate systems, thiol-ene reactions are less sensitive to oxygen inhibition and can produce materials with different mechanical properties depending on the ratio of thiol and ene components, enabling spatial control over stiffness within a single printed object.

16Advanced Science. Synergizing Algorithmic Design, Photoclick Chemistry and Multi‐Material Volumetric Printing for Accelerating Complex Shape Engineering

What Holds Volumetric Printing Back

For all its elegance, volumetric printing faces real constraints that have so far kept it mostly in the lab rather than on the factory floor. The most fundamental is build volume. Tomographic printing requires light to pass through the entire resin bath from multiple angles, which means the resin must be reasonably transparent at the curing wavelength. As the vial gets larger, light is absorbed and scattered more before reaching the center, reducing contrast and resolution. Most published demonstrations work with print volumes in the range of a few centimeters across.

Heat is another persistent problem. Free-radical polymerization releases energy, and when an entire volume of resin begins curing more or less simultaneously, the temperature spike can be dramatic. Temperatures rising more than 60°C above ambient have been reported during conventional volumetric prints, which can trigger auto-acceleration, where the reaction speeds up faster than heat can dissipate, degrading print fidelity and warping the final part.

17Nature Communications. Enhanced volumetric additive manufacturing via Reversible Addition-Fragmentation Chain Transfer (RAFT) polymerization

For continuous printing systems that build from a liquid interface, a related thermal issue arises: heat from the curing zone accumulates in the resin pool and limits how fast you can print before the uncured resin starts to gel prematurely. One solution that has shown promise is pumping a non-reactive fluorinated oil through the build interface to carry heat away during polymerization.

18Science. Rapid, large-volume, thermally controlled 3D printing using a mobile liquid interface

Material diversity is another limitation. Nearly all volumetric printing to date uses photopolymer resins, which tend to be brittle acrylates or soft hydrogels. The range of mechanical properties, thermal stability, and biocompatibility is expanding, as demonstrated by the glass-printing and thiol-ene chemistry work described earlier, but it remains narrow compared to the palette available for conventional manufacturing. Metals, high-performance engineering plastics, and composites are largely out of reach for now.

Resolution is also geometry-dependent. In tomographic printing, the best resolution is typically achieved for features at the center of the vial; features near the periphery or in regions where light must traverse more resin tend to be less sharp. The computational algorithms that generate the light patterns make trade-offs between overall print fidelity and local resolution, and artifacts from imperfect dose delivery can show up as unwanted cured resin or insufficiently cured regions. Holographic light engines have helped on this front, but the physics of projecting light through a scattering medium impose hard limits.

Printing Around and Inside Existing Objects

Overprinting deserves a closer look because it enables manufacturing workflows that are genuinely new, not just faster versions of what existed before. In conventional 3D printing, the object sits on a flat build plate and grows upward. There is no practical way to encase a pre-existing component inside a printed structure without pausing the build, placing the component, and hoping the next layers adhere properly. In tomographic volumetric printing, the insert sits in the liquid resin from the start, and the solidification pattern wraps around it by design.

This has been demonstrated with inserts of various shapes and materials, from simple cylindrical rods to complex geometries, with the computed projections adapted to account for refraction and absorption caused by the insert.

19PubMed Central. Volumetric additive manufacturing of complex geometries around complex inserts

Potential applications range from encapsulating fiber-optic sensors in protective housings to creating graded-stiffness interfaces between a rigid metal implant and surrounding soft tissue in biomedical devices. The ability to co-print multiple material systems, combining volumetric photopolymerization with extrusion of a secondary material or with pre-placed inserts, moves additive manufacturing closer to the kind of multi-material integration that injection molding and overmolding achieve in traditional manufacturing, but with far more geometric freedom.

20ACS Applied Polymer Materials. Multimaterial Vat Polymerization Additive Manufacturing

Where the Technology Is Headed

Several research threads are converging to push volumetric printing toward broader practical use. On the hardware side, holographic light engines are making it possible to print with higher resolution and less wasted energy. On the chemistry side, controlled polymerization strategies like RAFT are taming the heat problem that limits build size and material quality. On the software side, increasingly sophisticated algorithms are compensating for optical imperfections, scattering from cells or particles in the resin, and refractive effects from inserts.

The biomedical track looks particularly active. Printing soft, cell-laden constructs in seconds rather than hours reduces cell damage and opens the door to fabricating tissue models for drug screening, personalized implants, and eventually perhaps transplantable organs. The scattering-compensation techniques enabling printing at tens of millions of cells per milliliter are a significant step toward constructs that approach the cell density of native tissue.

For industrial applications, the most immediate niche may be custom optics and precision micro-components, where the combination of speed, surface quality, and geometric freedom gives volumetric printing a clear advantage over conventional alternatives. The millimeter-scale lenses produced in seconds with sub-nanometric roughness are not just lab curiosities; they represent a viable manufacturing route for prototyping and small-batch production of optical elements that would otherwise require expensive molds or slow polishing processes. Whether volumetric printing can eventually scale to the build volumes and material diversity needed for mainstream manufacturing remains an open question, but the pace of progress in the past five years has been faster than most observers expected.