The Evolution of High flow nozzles
How nozzle geometry changed filament heating, melting, and flow.
Why Nozzle Design Limits Printing Speed
Fused Filament Fabrication (FFF) or Fused Deposition Modeling (FDM) 3D printers can often move faster than their hot ends can melt filament. When the polymer reaches the nozzle outlet before its center is fully molten, extrusion pressure rises rapidly, the deposited flow becomes inconsistent, and the extruder may start skipping or slipping. The melt zone therefore sets a practical limit on the maximum printing speed.
The basic process has changed little since the first FFF systems. An extruder pushes solid thermoplastic filament into a heated print head; the material softens and melts, and the nozzle controls the final flow onto the part.
Figure 1. Fused Filament Fabrication (FFF) principle.
A typical hotend contains a heatsink, heat break, heater block, temperature sensor, and nozzle. These parts regulate where the filament remains solid and where it becomes molten. At higher flow rates, their most difficult task is transferring enough energy into the center of the filament before it leaves the nozzle.
How Filament Melts Inside a Hotend
Inside a 3D-printer hotend, the filament does not melt instantly. It passes through a controlled temperature gradient, starting in the cooled upper section where it remains solid, then moving through a transition region where the polymer gradually softens. The heatsink and heat break are designed to keep this transition zone as short and stable as possible, preventing excessive heat from travelling upward and causing heat creep.
As the filament enters the heater block, heat is transferred from the block and nozzle walls into the polymer. The outer surface of the filament melts first, while the inner core heats more gradually. As the filament moves farther down, an increasing portion becomes molten until it forms a viscous polymer melt inside the nozzle. The still-solid filament above acts like a piston, pushing this molten material towards the nozzle outlet.
The geometry of the melt chamber and nozzle strongly influences how efficiently this process takes place. Available surface area, thermal conductivity, filament residence time, flow velocity, and the distance over which heat can penetrate into the polymer all affect melting performance. At higher extrusion rates, the filament spends less time inside the hot zone, making efficient heat transfer increasingly important.
Finally, the molten polymer is compressed through the small nozzle orifice, where it exits as a continuous extruded strand. Understanding this melting process is fundamental to nozzle design, because improvements in heat transfer and melt distribution can directly increase the maximum achievable material flow rate while maintaining a stable extrusion temperature.
Four Principles to Increase Flow
Most high-flow nozzle designs use one or more of four recurring strategies.
The history of nozzle design is largely the history of applying these strategies with different geometries and manufacturing methods.
Increasing hotend temperature is not considered here. Although it can increase achievable flow, the benefit depends on the material and operating conditions and may require temperatures outside the material’s suitable processing range. Temperature is therefore treated as a tuning parameter rather than a substitute for improved hotend heat transfer.
The Conventional Nozzle and the Longer Melt Zone
The familiar V6-style nozzle provides a useful baseline. Its internal passage consists of a straight cylindrical channel followed by a conical transition into the extrusion orifice. Heat enters the filament through the surrounding wall. An early example of a threaded extrusion nozzle with a central flow passage appears in Stratasys patent US5121329, filed in 1989.
Volcano, SuperVolcano, Goliath, and other extended hotends improve throughput by lengthening the heated path. The filament spends more time in contact with the wall, and the larger contact area allows more energy to enter before extrusion.
Making the melt zone longer seems like an obvious way to increase flow: the filament simply has more time and more distance to absorb heat before it reaches the nozzle tip. But this also brings some unwanted side effects.
A longer hot zone means that more plastic remains molten inside the hotend. This can lead to more oozing and can make retraction and pressure control harder to manage. Because the nozzle normally points downward, a taller column of molten plastic can also make it easier for material to slowly flow out under its own weight.
So instead of simply asking how to make the melt zone longer, a more useful question is, how can we transfer heat into the filament more quickly and efficiently within the same, or even a shorter, distance?
This question is at the heart of many high-flow nozzle designs.
Patent Basics: Novelty and Validity
It is useful to understand what a patent actually protects. A patent does not protect a broad engineering goal such as improving heat transfer or increasing flow. It protects the specific technical features defined in its claims.
For a patent to be valid, several basic requirements generally have to be satisfied:
Novelty – the claimed invention must be new. The essential features of a claim must not already have been disclosed together in earlier prior art before the relevant filing or priority date.
Inventive step / non-obviousness – the invention must not be an obvious modification or combination of existing technology to a skilled person in the field.
Sufficient disclosure – the patent must explain the invention clearly enough for a skilled person to reproduce it.
Supported and definite claims – the claims must clearly define the invention and be supported by the patent description. Earlier patents, products, publications, and other public disclosures form the prior art
Prior art does not automatically invalidate a later patent simply because the same general principle was known before; the important question is whether the specific claimed combination of features was already known or would have been obvious.
A granted patent is also not automatically guaranteed to remain valid. Earlier prior art may later be discovered and used to challenge individual claims. In this article, patents are therefore used mainly as dated technical records to trace how nozzle-design concepts developed over time.
A Timeline of High-Flow Nozzle Ideas
Today’s high-flow nozzles did not appear all at once. Many of the ideas behind them developed gradually, sometimes in 3D printing and sometimes in other fields such as injection molding or multi-material processing.
The dates shown below are simply useful reference points. Depending on the example, they may refer to a patent filing, a patent publication, or the first public announcement of a product. They help show roughly when an idea appeared, rather than the exact moment it became commercially available.
1981–1988 – Conductive Torpedo Inserts
Heat-conductive torpedoes were already established in injection-molding nozzle design by the early 1980s.
US4652230, from 1985, describes a central heater needle (36) supported by a hub (38) containing multiple openings (56) through which the molten polymer flows. The solid portions of the hub provide a conductive heat path into the central needle, while the openings divide the surrounding melt flow. This increases the metal–polymer contact area and reduces the distance between the polymer and a heated surface.
Figure 4. Multiple-flow-passage torpedo arrangement. Source: US4652230A, Figs. 1–3.
A later example, US5028227, filed in 1988, shows a central torpedo (100) supported by radial fins (104) that divide the polymer into multiple flow channels.
These geometries bring conductive metal towards the center of the polymer path, reduce the maximum distance heat must travel through the material, and divide the flow into thinner regions. Although developed for injection molding rather than FFF 3D printers, they are useful historical examples of the same heat-transfer strategy later used in high-flow extrusion systems.
Torpedo insert top side view
Figure 5. Conductive torpedo example in an injection-molding nozzle. Source: US5028227A, Figs. 3–6.
Injection molding and FFF 3D printers are different manufacturing processes, but the local thermal problem inside a heated polymer passage is similar: energy must be transferred efficiently into moving thermoplastic. For this reason, injection-molding nozzle geometry is relevant as a technical comparison, and it is very relevant when studying earlier ideas.
1992 – Stratasys Internal-Heating Liquefier
US5340433 describes a Stratasys print head design that heats the plastic filament not only from the outside but also from the inside.
The system used a hollow plastic filament tube (250), passing through a heated nozzle. Inside the center of that filament was a metal core, often called a mandrel (282), connected to the hot nozzle body by four longitudinal ribs (284). Because this internal metal structure also became hot, the plastic was heated from both directions at the same time—from the outside walls of the nozzle and from the inside through the central mandrel. This reduces the maximum conduction distance compared with heating a solid filament only from the outside.
The design also increased the contact area between the hot metal parts and the plastic, further improving heat transfer and melting performance. Once fully molten, the plastic flowed around the small support ribs holding the center core and exited through the nozzle opening.
Although the design used hollow filament rather than the solid 1.75 / 2.85 mm filament common today, the engineering principle remains relevant: placing heated metal inside the polymer path can improve melting efficiency by shortening the distance heat must travel.
1993 – Spiral-Blade Torpedo
The design disclosed in EP0614746 / US5405258, US5318434A places a central torpedo (80) inside the polymer melt passage and supports it with spiral blades. These blades force the molten polymer to follow a helical path, creating a deliberate swirling motion as it approaches the nozzle exit hole (gate).
Compared with a straight flow path, the spiral geometry increases the effective distance travelled by the polymer and continuously redirects the melt. This promotes redistribution of material across the flow and can help reduce local temperature differences within the melted polymer. The patent itself emphasizes another important effect: the swirling motion reduces strongly unidirectional molecular orientation near the exit hole, resulting in a more uniform flow pattern and improved strength of the molded part.
The important additional idea compared with earlier torpedo designs is therefore that the internal geometry is used not only to divide the polymer flow or conduct heat towards its center but also to deliberately rotate and redistribute the molten material. This is an early example of using internal polymer-flow geometry to actively control the melt rather than simply allowing it to flow straight through the nozzle.
2009 – Stratasys Flat Filament
Stratasys publications, including US8221669 and US20110076496, describe non-cylindrical filaments used with a matching liquefier passage. Instead of using round filament, they designed a thin, flat filament and a hotend channel with the same shape.
The flat filament has a higher surface contact area with the hot metal, and its center is closer to the heated walls. Heat can therefore spread through the plastic more quickly and evenly. This could allow the printer to push material through the nozzle faster without leaving part of it insufficiently melted.
The design required both a special filament and a matching hotend, which limited its practical use. However, it demonstrated an important idea: changing the shape of the filament can improve melting and increase flow.
2014 – E3D Cyclops: A Related Multi-Stream Concept
E3D introduced the Cyclops in 2014 as a dual-extrusion hotend with two filament inputs, a shared melt chamber, and a single outlet nozzle. Its main purpose was rapid material or color switching rather than increasing melt capacity. A similar idea is disclosed in an earlier Stratasis patent, US5121329A (Figure 6).
Figure 9. E3D Cyclops was introduced for dual extrusion and rapid material switching.
Inside the Cyclops hotend, two separate molten filament streams are brought together before reaching the outlet. E3D presented this design mainly as a way to enable fast color switching while keeping extrusion pressure under control. Complete color mixing was a different challenge and was not the main purpose of the design.
Cyclops is therefore included here not as a dedicated high-flow nozzle, but as an early example of two melt streams being combined inside a single hotend. As a secondary effect, feeding the nozzle through two melt paths also increased the total amount of molten material that could be supplied to the outlet.
Other interesting multicolor blending projects:
2015 – Finned Injection-Molding Nozzle
US10821642B2 describes an injection-molding nozzle with longitudinal fins extending inward from the nozzle wall. The main purpose of these fins is to control the temperature of the polymer near the outlet and help reduce stringing, rather than to increase melting speed.
Figure 10. Inward-fin injection-molding nozzle geometry. Source: US10821642B2.
The geometry is still interesting from a high-flow perspective. By extending metal surfaces further into the polymer stream, the fins increase the contact area between the nozzle and the material and shorten the distance heat must travel through the polymer. Depending on which side is hotter, the same structure can either transfer heat into the polymer or remove heat from it. This makes the design a useful example of how internal nozzle geometry can be used to influence heat transfer.
2016 – Internal Core Heating and Bondtech CHT (2021)
EP3445568 describes heat-conductive material extending from the nozzle wall towards the center of the filament path. Illustrated forms include a diagonal bar and a central block containing multiple channels.
These structures transfer heat towards the filament center and can divide the polymer into smaller streams. Bondtech later commercialized CHT nozzles in 2021 after development work around Core Heating Technology, bringing this general strategy into a compact nozzle for conventional round filament.
The patent claims are written quite broadly. For example, Claim 1 generally covers a heat-conductive structure (7) placed inside the melt path to transfer heat toward the filament core. Claim 4 extends this concept further by describing a heat-conductive block positioned in the center of the flow channel without defining a specific shape or geometry.
Earlier patents had already disclosed internal conductive structures, torpedo-like elements, heated filaments from the inside and outside, and divided polymer flows. This raises an important question: if these concepts were already publicly disclosed years earlier, what is the actual new inventive step introduced by the Bondtech patent?
This does not necessarily mean that the Bondtech patent is completely invalid, but prior art can partially invalidate a patent or limit how broadly its claims can be interpreted. In practice, the patent may provide protection mainly for the specific nozzle designs and implementations described in the patent, rather than for the general idea of heating the filament from the inside or dividing it into several streams or adding a heat-conductive block inside the nozzle to improve melting capacity.
2020 – E3D Squeeze-Tube Liquefier (Later FUGE)
WO2021205174A1 and the related EP4132765 family describe a liquefier passage that transitions from a substantially circular inlet (151, 351) to a non-circular section (153, 353) and then towards the outlet. Examples include oblong, oval, polygonal, cruciform, and star-shaped sections.
Reshaping the filament reduces its local thickness and can increase contact surface area with the heated wall. The passage can maintain a similar flow area while changing shape, seeking to improve heat transfer without relying only on a longer melt zone.
Some variants also use successive non-circular sections with a rotational offset; the patent describes this arrangement as promoting mixing of the molten filament and improving thermal distribution.
E3D later used the FUGE (under development) name for a related high-flow concept and publicly described it in 2026 as flattening the filament to create a large heated surface area and a short conduction distance.
Using a non-round melt path to bring the heated wall closer to the center of the material is not, by itself, a new principle and can already be found in earlier patents. What is more specific in the E3D patent is the way this geometry is arranged inside an FFF 3D printer hotend.
The filament enters through a round passage, is reshaped into a non-round form through the central part of the melt path, and then returns to a round flow before reaching the nozzle outlet. Part of this sequence also follows naturally from the practical constraints of FFF 3D printing: standard filament is round when it enters the hotend, and the final nozzle orifice is normally round as well. The non-round section is therefore the part that deliberately changes the geometry to shorten heat-transfer distances within the material.
2022 – Bozzle Tungsten-Carbide Nozzle
The Bozzle takes a different approach. Instead of using a separate insert or several individual channels, the nozzle itself contains a single cross-shaped polymer passage formed directly into the tungsten-carbide body.
Figure 13. Bozzle tungsten-carbide nozzle and simplified cross-section
This shape changes how the material is distributed inside the nozzle. Compared with a conventional round bore of similar flow area, the cross-shaped passage creates more contact with the heated walls and reduces the distance heat must travel to reach the center of the polymer. In effect, the filament is spread into several thinner but still connected sections, allowing heat to reach the material more easily without adding a separate internal element.
The one-piece tungsten-carbide construction also provides high wear resistance and high-temperature capability. Public retail evidence confirms that the Bozzle was commercially available by late 2022.
2022 – Three Channel Insert Nozzles
By 2022, inexpensive high-flow nozzles from Chinese manufacturers had appeared using a different construction method. Instead of machining the three flow channels directly into the nozzle body, these designs used an enlarged conventional bore containing a separate copper insert with three off-center passages. The insert divides the incoming filament into three thinner streams while also conducting heat toward the center of the polymer flow.
Figure 14. Three-channel Insert nozzles
Later variants combined the same three-channel copper insert principle with hardened-steel nozzle bodies or tungsten tips, providing greater wear resistance while retaining the high thermal conductivity of the internal insert. These nozzles are an interesting example of how an established heat-transfer and flow-division principle can be implemented through a substantially different and lower-cost manufacturing approach.
Although commercially associated with the Bondtech CHT concept, the underlying strategy of placing conductive metal inside a polymer flow and dividing that flow into multiple thinner paths had precedents in much earlier extrusion and injection-molding designs (see Stratasys nozels and torpedo inserts).
2025 – Twist Flow Nozzle
The Twist Flow Nozzle (CN120134620A) uses a conductive outer housing (1) and two conductive inserts (21, 22) that enclose the polymer passage. The opposing insert surfaces form a changing, twisted cavity rather than a set of straight drilled channels.
The passage is designed to increase contact with heated metal, gradually deform the polymer into thinner regions, and move material through paths with different directions and local velocities. Recombination between these regions is intended to mix material at different stages of melting and produce a more uniform outlet temperature.
Figure 15. Twist Flow Nozzle housing and conductive inserts forming the internal twisted polymer passage.
In this way, the TFN combines several high-flow strategies within one nozzle: shorter heat-conduction distance, greater heated surface contact, controlled filament reshaping, increased residence path, and flow mixing. Its contribution lies not in any one of these principles individually, but in the particular internal geometry used to combine them.
Figure 16. Graphical illustration and simulation of the TFN nozzle melting flow mechanism
Comparison of High-Flow Nozzle Design Strategies
Implementation and historical context
Although high-flow nozzles can look very different from one another, most of them rely on the same basic ideas: giving the polymer more time to absorb heat, increasing contact with heated metal, reducing the distance heat must travel, splitting the flow into smaller streams, or improving how the molten material mixes.
The two tables below compare both the different designs and the ideas behind them. This makes it easier to see how similar engineering principles have appeared in different forms over time.
Cyclops is not included in the comparison because its main purpose was multi-material switching rather than increasing flow.
Design | Main geometry / concept | Thermal / flow principle | Significance in nozzle evolution |
|---|---|---|---|
Extended melt zone / Volcano | Long cylindrical melt path | Increases residence time and heated wall contact | Simple approach to higher flow by increasing melt-zone length |
Torpedo insert | Central conductive core supported by ribs | Brings conductive metal towards the flow center, reducing conduction distance and dividing the polymer into thinner regions | Established an injection-molding strategy by the early 1980s |
Spiral-Blade Torpedo | Central conductive torpedo supported by helical blades | Divides and redirects the melt into spiral flow paths, increasing the effective travel distance and creating deliberate swirl and redistribution. | An early example of using internal nozzle geometry not only for conduction and flow division but also for active control of polymer flow |
Stratasys mandrel | Heated central core inside hollow filament | Heats the polymer simultaneously from the outside and from within | Early FDM implementation of direct internal heating |
Flat filament | Ribbon-shaped filament with a matching passage | Reduces the maximum heat-conduction distance through the polymer | Uses filament geometry itself to accelerate heating |
Bondtech CHT | Internal conductive structure with multiple channels | Brings heated metal towards the core and divides the melt | Commercial 2021 high-flow implementation for round filament |
Bozzle | Integrated cross-shaped polymer passage | Raises the perimeter-to-area ratio and shortens the conduction path | Single-piece tungsten carbide; no separate internal insert |
E3D Squeeze Tube / FUGE | Round inlet transitioning to a flattened or non-circular passage | Reshapes filament to shorten conduction distance and increase contact | Patent priority 2020; FUGE publicly described in 2026 |
Twist Flow Nozzle (TFN) | Opposing twisted cavities formed around conductive inserts. | Increases contact area, shortens conduction distance, reshapes flow, and promotes mixing | Combines several established strategies in a different internal geometry |
Strategy matrix – how the same core principles reappear
Design | Longer flow path | Conductive insert / core | Reduced thickness / reshaping | Divided / split flow | Mixing / redistribution |
|---|---|---|---|---|---|
Volcano | Primary | — | — | — | — |
Torpedo insert | — | Primary | Primary | Primary | — |
Spiral Torpedo | Secondary | Primary | Primary | Primary | Primary |
Stratasys mandrel | — | Primary | Secondary* | Secondary | — |
Flat filament | — | — | Primary | — | — |
Bondtech CHT | — | Primary | Secondary | Primary | — |
Bozzle | — | — | Primary | — | — |
E3D FUGE | — | — | Primary | — | Secondary |
Twist Flow Nozzle | Secondary | Primary | Primary | Secondary | Secondary |
* For the Stratasys design, “reduced thickness” refers to the thin annular wall of the hollow filament rather than active reshaping of a round filament.
Primary = central mechanism; Secondary = contributing effect; — = not a principal feature. The matrix describes engineering function, not patent claim scope.
What the comparison shows
At the level of basic engineering principles, several modern nozzle concepts have clear similarities to earlier designs. Bondtech CHT uses inward conductive structures and divided flow paths, approaches that can also be found in earlier injection-molding torpedoes and in the Stratasys mandrel concept. E3D’s non-circular liquefier and the Bozzle Nozzle reshape standard round filament inside the hotend, while earlier Stratasys work had already explored thinner, non-round filament sections to improve thermal response.
TFN approaches the problem differently. Its internal geometry is primarily intended to improve heat transfer and melt performance, but the resulting flow also creates a redistribution and mixing effect inside the nozzle. In that sense, the behavior has some similarity to earlier spiral-torpedo designs, where the melt is deliberately guided through a more complex flow path before reaching the outlet.
Technical Appendix
The simplified models below explain the physical relationships used in the article. Real hotends include changing geometry, phase change, viscous flow, pressure-dependent contact, and transient heating, so these calculations are illustrative rather than complete performance predictions.
Figure 17. Simplified hotend model.
Fourier’s Law and the Design Variables
A simple conduction model relates heat-transfer rate to thermal conductivity, contact area, temperature difference, and conduction distance.
Q = kA ΔTd = ΔTRth
- Q is the heat-transfer rate in watts.
- k is the thermal conductivity of the material.
- A is the contact area perpendicular to heat flow.
- ΔT is the temperature difference driving conduction.
- d is the distance heat must travel through the material.
Thermal Resistance Model
Thermal resistance is the inverse of conductance. For a simple layer, resistance increases with material thickness and decreases with conductivity and area.
Rth = LkA
- Rth is thermal resistance in K/W.
- L is the material thickness.
- k is thermal conductivity.
- A is the cross-sectional area perpendicular to heat flow.
Worked Example: Copper, Brass and ABS
Using the simplified assumptions above, the calculated thermal resistance of the ABS layer is far larger than the resistance of the copper block or brass nozzle. The example omits interface resistance, convection, viscous dissipation, and the changing state of the polymer, but it illustrates why geometry inside the plastic path can dominate heat transfer in high-flow designs.
Layer | Thickness L | Thermal conductivity k | Area A |
|---|---|---|---|
Copper block | 5 mm | 385 W/(m·K) | 1 × 10⁻⁴ m² |
Brass nozzle | 2 mm | 120 W/(m·K) | 1 × 10⁻⁴ m² |
ABS layer | 0.9 m | 0.2 W/(m·K) | 1 × 10⁻⁴ m² |
As we can observe, even if the ABS layer is the thinnest, its thermal resistance is more than two magnitudes higher than that of the metal parts of the hotend. Therefore, reducing its thickness is one of the basic key idea for a high-flow hot end design.
Cylindrical Conduction Model
Real hotends are cylindrical or conical rather than flat stacks. A cylindrical resistance model better represents radial heat flow through concentric regions.
Here, rc is the inner radius, r1 – r3 are successive interface radii, k1–k3 are the thermal conductivities of the corresponding regions, and L is the axial length.
Even this model remains a simplification. Accurate performance comparisons require measured flow, pressure, temperature, material properties, and geometry under the same test conditions.
Sources and References
The references below support the dates, patent descriptions, and product-history statements used in the article. Patent databases provide technical records; manufacturer pages are used for product announcement and commercialization dates.
US4266723 — Nozzle for injection molding machines (1981)
US5028227A — Injection molding nozzle with replaceable gate insert
US4652230A — Injection molding nozzle (1987)
EP0614746 / US5405258 — Spiral-blade injection-molding torpedo with controlled swirl flow (1993)
US5340433A — Modeling apparatus for three-dimensional objects
US8221669B2 / US20110076496A1 — Ribbon filament and matching extrusion system
E3D — Introducing the legendary Cyclops and Chimera, 28 Nov 2014
US10821642B2 — Injection nozzle for an injection molding machine
EP3445568A1/B1 — Nozzle for a 3D printer, Carl Bernhard Beck
Bondtech — CHT high-flow nozzles release, 30 Sep 2021
WO2021205174A1 / EP4132765 family — Non-circular liquefier passage
E3D — The evolution of E3D’s high flow technology, 22 May 2026
Bozzle product evidence — Unique Prints listing with verified customer reviews from Dec 2022
Twist flow nozzle - TFN CN120134620A
AI disclosure: AI tools were used to assist with the creation and quality improvement of selected illustrations and with the review of the article text. AI-generated illustrations are conceptual and may not accurately represent specific products or internal geometries.