ThermalRouter: Enabling Users to Design Thermally-Sound
Devices
Alex Mazursky

Borui Li

University of Chicago
alexmazursky@uchicago.edu

University of Chicago
borui2000@gmail.com

Daria Shifrina

Joyce E. Passananti

University of Chicago
dshifrina@uchicago.edu

University of Chicago
joycep@uchicago.edu

Shan-Yuan Teng

University of Chicago
tengshanyuan@uchicago.edu

Svitlana Midianko

University of Chicago
s.midianko@gmail.com

Pedro Lopes

University of Chicago
pedrolopes@uchicago.edu

Figure 1: Three objects improved using ThermalRouter: (a) 3D-printed game console slowed due to CPU heat. (b,c) ThermalRouter
added thermally-conductive channels to route heat away from the heat source. (d) 3D printed dragon lamp melted at PLA’sheat deflection temperature; ThermalRouter created a version that didn’t buckle. (e) ThermalRouter can also be applied to soft
objects like a silicone phone case with embedded liquid metal channels.

ABSTRACT
Users often 3D model enclosures that interact with significant heatsources, such as electronics or appliances that generate heat (e.g.,
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UIST ’23, October 29–November 01, 2023, San Francisco, CA, USA© 2023 Copyright held by the owner/author(s). Publication rights licensed to ACM.
ACM ISBN 979-8-4007-0132-0/23/10. . . $15.00
https://doi.org/10.1145/3586183.3606747

CPU, motor, lamps, etc.). While parts made by users might function
well aesthetically or structurally, they are rarely thermally-sound.
This happens because heat transfer is non-intuitive; thus, engineering thermal solutions is not straightforward. To tackle this, wedeveloped ThermalRouter, a CAD plugin that assists with improving
the thermal performance of their models. ThermalRouter automatically converts regions of the model to be made from thermallyconductive materials (such as nylon or metallic-silicone). These
regions act as heat channels, branching away from hotspots to dissipate heat. The key is that ThermalRouter automatically simulates
the thermal performance of many possible heat channel configurations and presents the user with the most thermally-sound design

UIST ’23, October 29–November 01, 2023, San Francisco, CA, USA(e.g., lowest temperature). Furthermore, it allows users to customize
by balancing costs, indicating non-modifiable geometry, etc. Most
importantly, ThermalRouter achieves this without requiring manuallabor to set up or parse the results of complex thermal simulations.

CCS CONCEPTS• Human-centered computing → Human computer interaction(HCI); Interaction devices; Haptic devices; • Hardware → Emerging technologies.

KEYWORDS
thermal, heat, engineering, interactive assistant, CAD
ACM Reference Format:
Alex Mazursky, Borui Li, Shan-Yuan Teng, Daria Shifrina, Joyce E. Passananti, Svitlana Midianko, and Pedro Lopes. 2023. ThermalRouter: Enabling Users to Design Thermally-Sound Devices. In The 36th Annual ACM
Symposium on User Interface Software and Technology (UIST ’23), October
29–November 01, 2023, San Francisco, CA, USA. ACM, New York, NY, USA,
14 pages. https://doi.org/10.1145/3586183.3606747

1

INTRODUCTION

Advances in fabrication and computer-aided design (CAD) haveempowered users to create functional devices, from home media
players (e.g., printed enclosures for microcomputers such as the
Raspberry Pi), interactive clothing & wearables [10, 21], or evenadding 3D printed parts that improve the functionality of existing
appliances (e.g., [53]).
Unfortunately, while many 3D printed objects created by users
are mechanically functional & aesthetically pleasing, they are oftennaïve to thermal issues (e.g., heat loosens fits, slows down computation, and even melts plastic) because heat transfer is not an
intuitive phenomenon. Over the last decades, many learning scientists have researched how people (including children, young
students, and college students) develop an intuition for heat transfer (e.g., [9, 16–18, 31, 34, 36, 56], to cite a few). Researchers havefound that understanding the fundamentals of heat transfer can bedifficult even for university-level engineering students, even after
taking physics and thermodynamics courses [54]. One would not
expect non-engineers engaged with 3D printing (e.g., some makers& hobbyists) to be an exception to these findings. We also takeinterest in the challenge of understanding heat transfer; however,
our interest is not strictly pedagogical. Instead, we explore how a
3D editor may assist users, not only with creating shapes but alsowith incorporating thermally-conductive materials and structures
to alleviate their thermal issues.
Let us exemplify how even the thermal performance of the 3D
printed case shown in Figure 1 (a), which turns a Raspberry Pi into agaming console, has stark consequences for the interactive device’s
performance. As revealed in our Walkthrough, the 3D printed casetraps the CPU’s heat and causes its clock speed to slow down
after just one minute of intense computation (CPUs measure theirinternal temperature and adjust their clock speed to prevent thermal
failures). Unfortunately, designing a custom 3D printed case withthermal performance in mind is non-trivial.
Moreover, thermal issues can have other consequences, suchas an impact on structural stability or geometric fits. For instance,

Alex Mazursky et al.

heat buildup on regions of a user’s model made from plastics willcause the plastic to deform, especially under loads. These are justa few examples of possible thermal issues, which can negatively
impact objects that interact with heat sources. The challenge isthat while devices engineered by professionals undergo dedicatedengineering to address this, users do not have interactive tools that
directly support them in authoring thermally-sound devices.
Similarly, typical maker-friendly materials exhibit poor thermal
performance. The most accessible 3D printing material (PLA) isinherently insulating and exhibits a low melting point—this is normally seen an advantage, as it eases the printing process, but it
becomes a severe issue if the final printed object is exposed to heat(e.g., melting). In fact, nearly all plastics have poor thermal conductivity, leading to heat buildup within prints that interact withheat sources. Recently, 3D-printable thermally-conductive plastics
have come to market and have been used to develop heatsinks withcustom geometries. However, making entire objects from these
new materials is costly to users (i.e., typically 10x the cost of PLA).
Therefore, there is a need for an approach that allows users tobalance both cost and performance.
To tackle these issues, we engineered ThermalRouter, a CAD
plugin that assists in creating thermally-sound devices, as depicted
in Figure 1. We implemented ThermalRouter as a plugin to Autodesk’s Fusion 360, a popular tool for designing 3D-printed devices.
ThermalRouter improves the thermal performance of an object by
converting regions of the user’s model to be printed with thermallyconductive materials (such as thermally-conductive nylon or even
thermally-metallic-silicone, which enables applying our techniqueto soft models, too). While recent advances in computational design have led to optimal heatsink geometries [38, 57], these require
adding additional materials into users’ designs which can require
additional modeling to accommodate the design changes; in contrast, a benefit of our approach is that we embed the heat sink directlyin the user’s model so no additional material or 3D design is needed.
ThermalRouter’s key principle is that it simulates the thermal
performance of many possible design variations, which are generated not only from its heuristics but also incorporating the user’s
input, such as maximum allowed material costs, regions to avoid,location of heat source(s), and so forth. At each step, ThermalRouter not only presents the user with the most thermally-sounddesign, but also lets users explore any internally generated variations, which allows users to gain intuition from different thermal
designs or explore different aesthetics.

2

RELATED WORKThe work presented in this paper builds on the challenges of understanding heat transfer, advances in personal fabrication, especially,
3D modeling software with embedded domain knowledge, andthermally-engineered materials.

2.1

Heat transfer is unintuitive

First, to understand why ThermalRouter addresses an important
problem, one must establish that heat transfer is not an intuitive
phenomenon to grasp. Over the last decades, learning experts haveresearched how people develop an understanding of heat transfer(see [9, 16–18, 31, 34, 36, 56] to cite a few of these studies) and foundThermalRouter: Enabling Users to Design Thermally-Sound Devices

it poses “very significant difficulties [to the learner] in acquiring thenotion of temperature” [36]. Luce & Callanan studied conversations
about heat and temperature between parents and children (N=51),
suggesting that everyday language (words such as “hot” and “cold,”that tend to replace the complex nature of heat transfer, e.g., “heat”
and “gradient”) might play a key role in limiting our understandingof heat from an early age [43].
Numerous studies found evidence that heat transfer is nonintuitive across ages. Lewis & Linn found that adolescents, adults,
and scientists can display difficulties with heat transfer [36]. Robbins & Ardebel found that engineering students require years ofcollege-level study to develop an intuition on thermal transfer concepts [54]. Their findings (N=101) show that 2nd year engineeringcollege students (before taking a thermodynamics course) were only
able to correctly express 24% of heat conduction concepts, comparedto just 41% after taking their first thermodynamics course.
Altogether, these findings suggest that understanding heat transfer is difficult, even for university-level engineering students. As
such, one expects heat transfer to be a challenging phenomenon
for many more users that might cross paths with interactive fabrication, such as makers & hobbyists involved with 3D printing
and making—a domain in which heat-related challenges naturally
arise. To this end, Khounsary et al.’s analysis of heat transfer education denotes that the background required to solve heat-related
problems in engineering is a tall order for most users: “a practicing
engineer must have a reasonable understanding of design, analyses, materials, fabrication processes, etc., to be able to apply heattransfer know-how to the problem at hand” [31]. Finally, this study
specifically warns that “addressing thermal (. . .) issues will become
more difficult as the projects proceed along the design path” [31],suggesting that tackling heat should be done early in the process,as well as continuously if possible.

2.2

Personal fabrication and thedemocratization of do-it-yourself (DIY)

Personal fabrication enables end-users to make their own interactive devices [7, 23]. Personal fabrication rocketed with the availability of low-cost CNC tools (e.g., 3D printers, laser cutters, cutting plotters, etc.) aimed at makers & hobbyists. To accelerate this
explosion in end-user tools, researchers often develop hardware
and software methods for democratizing making and fabrication.
Since our work is software-based, we will focus on tools that assist the user by directly embedding domain knowledge inside thecomputational-aided design software (CAD).

2.3

Embedding domain knowledge inside CAD
Editors

Beyond speeding up the user’s iteration cycles, many researchers
have focused on understanding how to lower the knowledge barrier
required to manufacture objects or use CAD functionality. This isespecially relevant for techniques that build on more advanced
know-how and would otherwise require a degree in mechanicalengineering or related fields [42, 51]. To this end, many researchers
explore how to embed domain-specific knowledge inside the CAD
environment.

UIST ’23, October 29–November 01, 2023, San Francisco, CA, USA

Several recent works have successfully embedded knowledge ofstructural mechanics into users’ designs to make them structurallysound, i.e., prevent the user’s resulting objects from collapsing under heavier loads. For instance, ShapeStructuralizer integrates arecommender system in a wireframe design tool to inform users ofalternate designs that satisfy stress constraints [15]. FastForce automatically identifies laser-cut structures that would normally break
and reinforce them in real-time [1]. Forte let users easily sketch out
2D structures, which then served as the basis for generative designs
that reinforce and make them structurally viable [13]. TrussFab[32] and TrussFormer [33] integrated structural & dynamical analysis into an editor, allowing users to create stable large-scale andeven animated structures. Moreover, others embed knowledge ofmaterials into editors [26]. Metamaterial Mechanisms is an editor
with metamaterial cells that can be assembled into machines [29],this is supported by a simulator that assists users while designingthese otherwise unintuitive mechanisms. Along similar lines, users
benefit from editors with domain knowledge of shape-changing
materials [2]. In fact, embedding domain-knowledge directly inside the CAD editor is so paramount that many subfields beyond
mechanics/3D-printing have been approaching this challenge too,such as magnetics [48], electronics [64], aerodynamics [61], acoustics [60], animation [30], paper crafting [49], and so forth.
While several domains have benefited from embedding domain
knowledge into editors, to the best of our knowledge, there is no
exploration on how to assist users with their model’s thermal performance. Simultaneously, problems arising from heat sources orpoor thermal performance have plagued both students [31] andresearchers when designing, for instance, wearable devices [58] orprofessional machinery with custom heatsinks [57].

2.4

Thermally-engineered materials and devices

Materials with high thermal performance have long been studied inmaterial science for their ability to regulate heat flow. While, metals
traditionally shined for thermal conductivity (e.g., typical heatsinks
added externally to most machines [4, 8]), polymer composites
with thermally-conductive fillers have recently gained attention
for their low cost and electrical insulation [57]. While the plastics,
used in most personal fabrication machines (e.g., laser cutters or
3D printers), have poor thermal conductivities (∼0.1-0.5 W/m-K)[3], they can be improved by blending conductive filler particles
in the filament (such as carbon fiber, ceramics, conductive nanomaterials, and more [12, 14, 24]). These composites have thermal
conductivities orders of magnitude greater than the base plastic (∼230 W/m-K). Recently, composites have been tuned specifically forfused filament 3D printers [35, 52]. The recent commercialization ofthese thermally-enhanced filaments (e.g., the ICE9 thermal filament[66], which we use to demonstrate some of the tool’s functionality)
has brought these materials into maker spaces [57]. However, CAD
tools are not directly supporting users with the required domain
knowledge to make use of the thermal performance of these thermal
filaments.
While 3D printing is still primarily used to fabricate rigid objects,
other techniques (e.g., casting or molding) are used to make soft
objects (e.g., covers for smartphones or wearables), which must
conform to the target shape. To this end, materials like silicone

UIST ’23, October 29–November 01, 2023, San Francisco, CA, USA

Alex Mazursky et al.

Figure 2: (a) A user models a custom handheld gaming case for their Raspberry Pi. (b) However, after printing and playing agame for a few minutes, they notice their framerate reduce (performance curve generated with stressberry, a standard test usedby Raspberry Pi community to measure CPU temperature [47]) and (c) that the back of the case has become hot to the touch.
are used for their ability to conform/stretch. Unfortunately, likerigid polymers, silicones have poor thermal conductivity [6]. Aswith plastics, researchers have doped these soft materials withthermally-conductive particles to improve thermal conductivity[46]. However, rigid fillers result in a material that is less conformable than undoped silicone. To develop a material that is both
soft and thermally-conductive, researchers mix silicone with eutectic gallium indium (EGaIn), a liquid metal alloy at room temperature.
This enhances the thermal conductivity of silicones by up to 25x [6,25, 28]. Inspired by these, we use metallic silicone to enable ourusers to produce soft objects with increased thermal performance(which we call soft heat channels).
Finally, in addition to thermally-conductive materials, recent research has shown the benefits of alternative structures for heat transfer, such as computationally optimized andbiomimetic/origami heatsinks [22, 38, 41, 44, 55, 62]. We leverage
this research on the effectiveness of branching patterns in our own
algorithm [37, 39, 63]. However, these methods are not user interfaces like ThermalRouter. These methods are algorithms applied to
specific engineering domains. These do not support users and only
cater to engineers and researchers that know how to implement
them to specific scenarios. Instead, ThermalRouter is the first to
assist users with their design’s thermal performance. Therefore, it
offers interactive support relevant to makers’ needs (e.g., balancecost of materials, simple fabrication process, etc.).

3

WALKTHROUGH

To give the reader a complete picture of how ThermalRouter enables
users to design thermally-sound devices, we present an example ofa user designing a handheld gaming case for their Raspberry Pi.
We chose this object as our first example for three reasons: (1) it
depicts a popular use of personal fabrication (thousands of hobbyists make custom cases like this); yet illustrates how even a simple
object can hide serious thermal issues (so drastic these affect the actual CPU performance and comfort); (2) the geometry of this game
console is not overly complex, which aids in understanding ThermalRouter’s output—note we show the contrast of ThermalRouter’s
output (black thermal filament) with the unmodified (printed inwhite filament); yet, if the user wishes for a uniform appearance,these could be printed entirely in the same color as the thermal

filament, painted over, or the thermal filament may be hidden inside the object’s shell; and (3) finally, the game console provides
an example of an object that lends itself well to iterations, illustrating that ThermalRouter is useful through different phases of a
prototype.
At the start, our user creates a version of their cat-shaped gamingcase by modeling around existing Raspberry Pi and electronics
models in Autodesk Fusion 360, as depicted in Figure 2 (a). However,after printing and assembling their design, they notice that the backof their case is hot to the touch, and the game’s framerate is reduced
dramatically after gaming for a few minutes, as shown in Figure 2(b, c).
Selecting a problematic heat source. As the user turns off
the console and touches the Raspberry Pi, they realize the heatsource is the CPU, which overheats when enclosed or used withouta heatsink. Similarly, they could also inspect for heat sources using
a thermal camera, as shown in Figure 2 (c) (all thermal images
taken with a FLIR C3). In the thermal image, this hotspot is 47°C.
To resolve this, our user runs the ThermalRouter plugin within
Fusion 360 and indicates that this CPU is heating up to 80°C (notethere are several ways a user can obtain a temperature, such as
estimates from the Raspberry Pi’s datasheet, with a thermal cameraor thermometer, or the CPU’s internal log). To select a heat source in
ThermalRouter, users select a 3D part and indicate its temperature
or wattage, as depicted in Figure 3.
Configuring and running ThermalRouter. Next, ThermalRouter needs to know which of the model’s regions it is allowed tomodify by embedding heat channels, which will be printed withthermally-conductive filament. The user selects both the top andbottom of the case to be modified. This freedom is critical as itallows users to (1) run ThermalRouter on subsets of a model (e.g.,
useful for iterations, large models, etc.) and (2) provide users with
control of where ThermalRouter places thermal material (e.g., foraesthetic purposes or to avoid specific areas). Next, the user selects
the outer surfaces of the case (those that are in contact with outsideair); these inform the simulation of surfaces that naturally convect
heat into the environment.
By selecting “advanced controls,” users can input (optional)
parameters to achieve better solutions, shown in Figure 4. For
example, they can: (1) Adjust the number of variations that

ThermalRouter: Enabling Users to Design Thermally-Sound Devices

UIST ’23, October 29–November 01, 2023, San Francisco, CA, USA

Figure 3: User input pipeline for improving the thermal issues on this Raspberry Pi case using ThermalRouter.

Figure 4: ThermalRouter allows users to provide (optional) input to generate better solutions, such as (a) number of iterations,(b) specific temperature goals, (c) cost of materials, (d) air speed, (e) rigid vs. soft output, and (f) customize the thermal materials.
ThermalRouter generates and preview each one—this saves timeby letting the user recognize if they would like to make further
changes before running ThermalRouter’s simulation. (2) Specify
ThermalRouter’s goal, such as reducing the maximum temperature or smoothing the thermal gradient (see Implementation for
details). (3) Adjust the expected cost of the thermal material
used via a slider–this adjusts the volume of the thermal material
devoted to the heat source—this gives users control over their budget and strikes an appropriate balance between material cost andthermal performance. Moreover, to improve the accuracy of theirsolutions, users can indicate (4) whether their objects will interact with circulating air, which allows ThermalRouter to simulate
convection—in this game console example, our user chose “no air”
since it is only exposed to still air (later we will depict examples
that make use airspeed). Also, the user can choose whether theyare (5) printing a rigid model or creating a mold for a soft
shape—our user chose “rigid” for the console (we depict later how
ThermalRouter generates molds automatically for silicone-basedmodels). Finally, if the user plans to use a thermally-conductive
material other than our default materials, they can (6) add custom
thermal materials.
ThermalRouter generates variations. After choosing the heatsource (and any optional settings), ThermalRouter automaticallygenerates many variations (see Figure 5) of this case with regionsof the geometry converted to print in a commodity filament withhigh thermal conductivity. These channels, depicted in a darker
color, extend outwards from the heat source to spread heat, likeconventional heat pipes. Finally, ThermalRouter shows the user themodel that performed best in simulation, e.g., the model with thelowest maximum temperature (see Implementation for details). Importantly, ThermalRouter balances cost and thermal performanceby only printing specific regions from thermally-conductive filament, rather than the entire object (as previously described, users
can tune this balance via our GUI). After simulating, users can selectthe variation to view from a drop-down list.
Iterating upon the output of ThermalRouter. The user inspects the result of ThermalRouter’s simulation of the design thatmost reduced the CPU’s temperature and is satisfied by the improved thermal performance: the hot spot is gone. However, the heatchannels also direct heat toward the pause button at the top of thedevice, which heats to 33°C (as shown in Figure 6 (a)) and will be undesirably warm to the touch. As such, the user navigates backwardin their timeline (a feature of modern parametric CAD software like
Fusion 360 that captures the step-by-step edit history, allowing tomodify or undo operations) and splits the case by sketching a circular boundary around the button. Now, when they navigate forwardin the timeline to update the design with ThermalRouter’s changes,
these regions are left unmodified by our channel algorithm, thus
avoiding the button (as shown in Figure 6, it is now at 27°C). In 3D
modeling, there are often alternative ways to achieve the same goal;
the same is true for ThermalRouter. In this situation, the user could
have also removed the heat channels around the button from theextrusion profiles used by ThermalRouter—this is possible because
all geometry generated by ThermalRouter is added to the model’s
timeline and is completely editable.
Gaining insights by stepping through ThermalRouter. The
user can review all the solutions created by ThermalRouter (rather

UIST ’23, October 29–November 01, 2023, San Francisco, CA, USA

Alex Mazursky et al.

Figure 5: ThermalRouter compares simulations on the baseline and many variations to find the best thermal solution.

Figure 6: The user keeps iterating on their case to perfect its thermal behavior, this time preventing heating the top button,
as well as editing ThermalRouter’s paths directly to influence the design’s aesthetics (ThermalRouter shortened to “TR” forbrevity).
than letting it automatically pick one), which allows users to prioritize other qualities, such as aesthetics. The user can also recover theoperations that generated the model and edit the channels’ geometry by accessing ThermalRouter’s sketch. For example, they canadjust the channels so that both cat ears have a stripe. To do this,they can simply modify the sketch, and the model is automatically
updated, as shown in Figure 6 (e, f).
Using ThermalRouter at different prototyping phases. Solving a single thermal problem does not have to be the end of interacting with ThermalRouter. Here, our user continues to build on
top of the design already modified by ThermalRouter. They now
model grips at the back of the case that contain rumble motors for
haptic feedback, as shown in Figure 7. They notice that the motors
are also a heat source and use ThermalRouter to address it. They
select the heat sources and parts to modify (the motor grips andthe back of the case), and ThermalRouter embeds additional heatchannels into the model. As always, ThermalRouter simulates thecase’s performance, including the existing channels, as well as the
new channel variations to cool the motors.

Fabrication. Satisfied, the user prints their final design by printing the case from PLA with embedded heat channels from thermallyconductive nylon. As shown in Figure 8, the thermal performanceof the case has improved as the CPU idles at lower temperaturesand does not throttle as rapidly under extreme stress. Moreover,the motor grips do not overheat on the user’s hands. While weused white PLA to visually contrast the heat channels from standard 3D printing materials, the user has several options to makechannels less visible: (1) print the PLA with a color that matches
the thermally-conductive filament’s color; (2) hide the channels
within the design by thickening the shell surrounding the entire
part; (3) post-process the print by painting it. In addition to therigid design highlighted in this Walkthrough, ThermalRouter also
supports making thermally-sound soft and stretchable devices.
For example, the user can choose to add a silicone sleeve to theback of their case that makes it comfortable to grip, but also aids inheat dissipation.

ThermalRouter: Enabling Users to Design Thermally-Sound Devices

UIST ’23, October 29–November 01, 2023, San Francisco, CA, USA

Figure 7: (a) The user continues to edit their handheld console design by drawing and attaching grips with vibration motors to
attach to the back of the case. (b) The user then runs ThermalRouter again, selects the motors as heat sources, and indicatesthat the grips and bottom of the case can be modified by the tool. (c) ThermalRouter simulates the baseline performance,
which reveals a hotspot forming on the grip. (d) ThermalRouter then presents the user with the design that best reduces the
maximum temperature.

Figure 8: (a) The user 3D prints their new case designed with ThermalRouter. Compared to the naïve PLA design (transparent
curves), the new case yields lower CPU temperatures and higher clock speeds. (b) Similarly, ThermalRouter addressed theissues of heat buildup on the back of the case, as well as on the motor grips. (c) Users can also print their case with black PLA tobetter hide the thermal channels for aesthetic reasons. (d) ThermalRouter also supports designing thermally-sound soft objects.

4

CONTRIBUTION AND LIMITATIONS

Our key contribution is that we proposed and developed a CAD
plugin to assist users with producing thermally-sound devices. We
implemented our concept as ThermalRouter—which we believe isa first step exploring embedding thermal knowledge in a CAD
editor. Using ThermalRouter results in several benefits for users,
such as time and money saved through less physical iteration, notto mention more thermally-sound solutions. To further refine thegenerated solutions, ThermalRouter considers user input, such as
the location and temperature of heat sources, the user’s goal (e.g.,
reduce temperature, smooth heat distribution, etc.), regions thatshould not be modified, faces exposed to outside air, speed of air, andeven expected material cost. Then, ThermalRouter automaticallysimulates many configurations of their design with embedded heatchannels and returns the design that best meets their goals without
the need to manually set up complex FEA simulations. Notably,users can also directly edit ThermalRouter’s output because it uses
existing CAD operations, unlike prior work that did not centeraround the user and their UI.
ThermalRouter is not without limitations. While our solutions
might outperform a naïve baseline in a range of scenarios, oursolutions are not necessarily optimal (our primary goal was assisting users with producing thermally-sound devices, rather than
optimality), since these are based on both our heuristics (e.g., creating channels outwards from heat sources) and simulation (e.g.,
Fusion 360’s FEA-based heat simulation), which merely approximates the real world. Combining our user-centered approach with
iterative, goal-seeking algorithms or machine learning may push
ThermalRouter into wider territory, such as via the methods used in[19, 38, 41]. However, we want to emphasize that our goal was not todevelop optimal solutions; this has been handled exceptionally wellin fields like numerical methods and optimization. However, thesemethods are not in-editor assistants. We explored a CAD editor thatassists users with designing thermally-sound objects. Moreover,other techniques that drastically alter the object’s form (e.g., generative approaches for custom heatsinks) may also be effective ataddressing thermal issues but come with their own challenges of
having to remodel around the added heatsink geometry. Instead,we designed ThermalRouter to preserve objects’ geometry, i.e., weonly convert existing regions to conductive materials, but do not
add new geometry. This is beneficial because the original design
is virtually unchanged, which minimizes the negative impact ondesired form factor (i.e., users do not need to drastically remodelto account for new geometry, and our thermal channels can be

UIST ’23, October 29–November 01, 2023, San Francisco, CA, USA

visually hidden by, for instance, burying the channels inside thedesign by expanding the object’s shell after ThermalRouter).
Finally, ThermalRouter addresses heat with passive cooling techniques (i.e., dissipates heat without requiring additional energy)
because these lend themselves well to the maker community (noneed for additional circuits, coolant fluids, or fans). However, there
is a range of more demanding heat systems, such as model engines
or gaming rigs, which rely on active cooling and are therefore notaddressed by ThermalRouter.

5

IMPLEMENTATION

We implemented ThermalRouter as a plugin for Autodesk Fusion
360. This provides ample opportunities for distributing our tool
to users engaged with 3D modeling physical prototypes, including other researchers and the maker community—to this end, we
provide all our code, test models, and scripts as open source1 .
Overview. To implement ThermalRouter, we used two programming environments: (1) Fusion 360’s Python interpreter, which weused to implement all the algorithms that create the heat channel
geometry, run iterative simulations and parse their results; and (2)Fusion 360 API [5], which provided access to the GUI functionality
we used to implement ThermalRouter’s user-facing dialogs andallowed access to scripting Fusion 360’s Finite Element Analysis.
Finite Element Analysis. Fusion 360 provides Finite Element
Analysis (FEA) tools that simulate structural mechanics, as wellas thermal simulation. Unfortunately, Fusion 360’s thermal simulation is intended for manual use by experts, i.e., before a user
can simulate the thermal performance, they are required to define each part’s material, generate contacts, define thermal loads,
and finally mesh the model before they can simulate. Thus, setting up an accurate simulation requires domain knowledge of heattransfer’s non-intuitive mechanisms (assigning appropriate values
for conduction, convection, and radiation). Every step introduces
opportunities for errors, such as inaccurate boundary conditions,
incorrect contacts, or flawed meshes, any of which can lead to unrealistic results, such as infinitely cold/hot parts and even crash
the simulation. Debugging these processes can take hours, even forexperts.
ThermalRouter automatically sets up FEA for the user’s
model. Instead, ThermalRouter simplifies this manual work andautomatically sets up thermal simulations on the user’s model.
ThermalRouter only requires the user to select which parts areheating up and indicate their temperature (°C) or power (W), as
well as indicate the faces of parts in contact with the outer air. Then,
ThermalRouter executes the remaining setup for simulations in the
background, allowing it to perform many simulations to find thebest performing design. The user can determine the temperatureand power of the heat sources by examining component datasheets.
Or, if the user has access to a temperature probe, infrared thermometer, or thermal camera, they can record the heat source temperatureduring operation.
Now we describe how we implemented ThermalRouter. For clarity, we describe in detail only the key components, while the moretrivial components, can be found directly in our open-source code1 .
1 Code, models, print settings, & guides: https://lab.plopes.org/#ThermalRouterAlex Mazursky et al.

5.1

Selecting regions of the model that will beprocessed by ThermalRouterNow, the user selects the regions in which ThermalRouter will
operate, by selecting parts with their cursor. Internally, ThermalRouter uses Fusion 360 API to create this collection of parts. We
do so via the args.command.commandsInput API, retrieving mouseselections via addSelectionInput(), and filtering the selected faces
with addSelectionFilter(). Using this process, ThermalRouter holds
an internal representation of the regions that it will use for thermal
improvements.

5.2

Routing heat channels

To route heat away from a target source, ThermalRouter uses a
straightforward geometrical hub-and-spokes approach (inspiredby modern & effective branched heatsinks [37, 39, 50, 63]), which
we depict in Figure 9 it directly connects the faces of the user’s
model with a 3D shape, representing the shortest path from theheat source to the environment. To realize this, ThermalRoutercreates arbitrarily long 3D spokes that branch away from this 3D
connection between heat sources and the faces of the model. These
spokes are then used as the splittingTool to split the parts selectedusing splitBodyFeature. This results in partitioned regions that areconverted to thermally-conductive material in both the design andsimulations. While this approach that branches heat channels out
from source to drain is simple and just one of many possibilities, it
is effective for heat transfer and is popularly used to spread heat inelectronics [11] and next-generation heat sinks [41].
Generating variations. Again, ThermalRouter is not attempting to find a final solution in one shot since we found early on you
cannot easily generalize to all models. Instead, it uses straightforward heuristics to create many variations of these spokes, simulates
their thermal performance, and judges them against each other. In
fact, the width and number of these spokes are the key parametersthat ThermalRouter varies across the different iterations as wellas the cost that the user is willing to spend (cost corresponds tothe channels’ maximum volume). The channel generation process
takes only a few seconds per iteration, though simulating each thermal solution is more time consuming (depending on the model’s
complexity, ∼1 minute for the gaming case shown in Walkthrough).
Therefore, we allow users to adjust the maximum number of iterations manually (or they can leave it at ThermalRouter’s default of
10 iterations).
The range of channel widths was chosen based on computational& empirical tests. We printed test objects (simple geometries andgeneralizable heat sources, such as in Figure 10) that let us determine that 2-20mm were the most useful widths—the lower bound
was set by how reliably channels could be printed with adequate
material, while the upper bound was where we found the area nearheat sources (of typical size for a 3D printed solution to work, i.e.,
up to 30mm) to start to be made entirely from Nylon, which would
be both costly & trivial. Therefore, we balance the number of spokes
with the width of the channel: as the number of spokes increases,
the channel width decreases. This keeps the amount of materialand costs across iterations similar. Adjusting the cost parameter
also adjusts the baseline channel width.

ThermalRouter: Enabling Users to Design Thermally-Sound Devices

UIST ’23, October 29–November 01, 2023, San Francisco, CA, USA

Figure 9: Main steps involved in our heat channel generation process. For simplicity and visual clarity, we depict it on theexample of a single heat source in our Raspberry Pi case model.
Assigning material properties. Before each of ThermalRouter’s variations are simulated, ThermalRouter uses the TargetBody.material property to assign different material properties
to the regular 3D printed or silicone regions and to the thermallyconductive regions (dark regions in Figure 9). If ThermalRouter iscreating rigid heat channels, it assigns the material properties of
the ICE9 material; conversely, if ThermalRouter is creating soft heatchannels, it assigns the metallic-silicone material properties. These
are our defaults, but ThermalRouter can run any other material theuser has in their material database if indicated to ThermalRouterin “Advanced options”.
Estimating material costs. At this step, ThermalRouter also
calculates the cost of the materials by retrieving the volume of thethermal regions and multiplying by their cost per volume. Thus,
users are given an estimate of the cost of each solution not only
before they spend time fabricating, but also before they spend timerunning simulations.

5.3

Simulating heat transfer

We implemented ThermalRouter to execute as much of the heatsimulation as possible without the need for user interaction. We
designed ThermalRouter this way since setting up a finite element
analysis (FEA) simulation that usefully approximates a real-world
heat transfer is not an easy task for users. At the end of any ThermalRouter process users can still open Fusion 360’s simulation
panel and browse through the results of each iteration simulatedby ThermalRouter to gain insights.
Heat sources. The first step of our automation for setting up athermal simulation is defining the heat sources: (1) ThermalRouter
iterates over all objects in the CAD scene: if a part was marked by
the user as a heat source, it is converted to a thermal load in thesimulation; (2) for the volume of each heat source, ThermalRouteralso adds its relative power by converting the temperature provided

by the user (e.g., 80ºC in our Raspberry Pi CPU in the Walkthrough)to watts using the specific heat formula; and (3) if the user specified
the room temperature in “advanced options,” ThermalRouter sets
this as the simulation’s environmental temperature, otherwise it
assumes 20ºC as a default room temperature.
Non-heat sources., ThermalRouter also automates the setup
for all non-heat source objects in the CAD scene, as follows: (1)iterates over all objects and sets the material properties they havebeen assigned—materials might be specified by the user or fromdefaults (e.g., PLA is default) or by the output of ThermalRouter
itself (e.g., rigid heat channels default to ICE9 Nylon, while softheat channels default to a 50-50 volume mixture of silicone and
EGaIn; both of these materials which we detail in our Material
Evaluation can also be specified by the user to any other material if
present in the material library); (2) assigns to each object’s surface
a radiation thermal load that matches the environmental temperature, i.e., in our simulations, non-heated objects start at thermal
equilibrium with their surroundings. (3) ThermalRouter sets theemissivity coefficient for all its custom materials (ICE9 Nylon, silicone, and metallic-silicone) at 0.9, as it is typical for plastics andrubbers [27, 45]; (4) now to properly simulate a more realistic heattransfer where the object is also surrounded by air, ThermalRouteradds natural convection thermal loads (i.e., heat transfer into still
air at previous room temperature) to all surfaces with a convection
coefficients at 2.50 W/m2 K, an approximation of convection in stillair [40]; (5) finally, after assigning these thermal loads to all objects,
ThermalRouter ensures contact between all surfaces separated byless than 0.10 mm, enabling conduction between material regionsthat are touching.
Materials settings. We introduced all the material parameters
needed to simulate ThermalRouter’s techniques. Much like all ourcode and tools, we provide these as an open-source material library1 .

UIST ’23, October 29–November 01, 2023, San Francisco, CA, USA

Alex Mazursky et al.

Table 1: Material properties of our common and thermally-conductive materials used in ThermalRouter’s simulations.
Material

Density (kg/mm3 )Thermal conductivity (w/m•K)

Specific heat (J/kg•K)

PLA (polylactic acid) [59]ICE9 (nylon-based) [66]silicone [20]metallic-silicone [6]1.25×10-06

0.13
4
0.2
4.7

1800
1100
1200
750

1.45×10-06
1.07×10-06
3.66×10-06

Figure 10: ThermalRouter generates and simulates many candidate versions of designs for each solution, then presents theuser with the design that best matches their chosen goal (e.g., lowest maximum temperature or smoothest thermal gradient).
Table 1 summarizes the key material settings we used in this paper,
obtained from manufacturer’s datasheets and the literature.

5.4

Picking the best result of a simulation

Now that Thermal Router generated many solutions for the user’s
model and has simulated each solution’s thermal performance, it
picks the best of these depending on the user’s goal. We provide
users with five methods to pick thermal simulations: (1) reduce
the highest temperature picks the solution with the lowest maximum temperature —this is our default, unless the user specifies
differently in the “advanced” settings; (2) smooth the heat distribution picks the simulation result that has the lowest thermal
gradient, i.e., where there is low temperature change from one
region to another—this is useful, for instance, for smoothing hot
spots for wearables (e.g., Figure 10); (3) increase the highest temperature—useful in designs that try to maximize heat at a spot,e.g., a heating device using resistive heaters; (4) reduce the minimum temperature—e.g., a cooling device using Peltiers; and (5)sharpen the heat distribution, which maximizes gradients—e.g.,
an insulated cup. To compare the simulation results, ThermalRouterparses each vertex of the FEA simulation output file to extract thetemperature and magnitude of the thermal gradient at that vertex.
It randomly samples 10,000 temperature points (for speed, since
thermal simulation data can be extremely large, up to a million samples). Then, since Fusion 360’s FEA simulation operates on coarse
meshes to optimize for computation speed, it also often producessome outliers, i.e., points where the temperature is extremely highor low (usually physically impossible temperatures). To filter theseoutliers, ThermalRouter discards the hottest and the coolest 1000
points. The remainder 8,000 points are then sorted by increasing

value. Finally, it ranks solutions by comparing the highest/lowest
temperatures/gradients, as specified by the user. To illustrate this,Figure 10 shows ten simulations on the baseplate of a wearable
device with three heat sources. As the user chose “smooth heat
distribution”, ThermalRouter picked variation #4, which presents
the most homogenous heat distribution, often desirable in wearables that touch the skin. Instead, had the user stuck to the defaultof “reducing the highest temperature” ThermalRouter would havepicked variation #8, which presents the lowest peak temperature—
this might be ideal for most cases, but perhaps not for this wearable
device.

5.5

Automatically generating silicone molds(for soft objects)

If the user is fabricating a soft object (e.g., from silicone), ThermalRouter will not only add these conductive regions to the model(same process as for the rigid channels) but also automatically generate and output the 3D print files for molds. As depicted in Figure
11, users fill these molds with silicone and metallic-silicone.
Mold generation. For each part that requires a mold, the following is performed to generate the mold automatically. First, theuser is prompted to select the open face of the mold. This region
will be left open so that silicone may be cast directly inside. Then,
ThermalRouter creates a copy of each silicone part; this copy isthen made 0.5 mm thinner by applying ExtrudeFeature with theopen face on the copied part as input, followed by a CutOperation.
This step is necessary to produce a 0.5 mm layer of silicone onto
which the metallic-silicone may be cast, as depicted in Figure 11.
Next, the copy is split using the same method described in Section
5.2; however, after performing the split, the regions which are notThermalRouter: Enabling Users to Design Thermally-Sound Devices

UIST ’23, October 29–November 01, 2023, San Francisco, CA, USA

Figure 11: (a) When working with 3D models to be cast in soft materials, such as silicone, ThermalRouter generates all themolds. (b-e) Users may then print the molds, cast with silicone, and glue into soft assemblies.

Figure 12: We characterized the thermal performance of the materials used in all examples of ThermalRouter.
made from metallic-silicone are removed. Then, a shell is createdfrom the part’s geometry by calling ShellFeatures with the open face
as input. The shell’s thickness is set to 2 mm, which is the mold’s
wall thickness. Finally, the shell is combined with the copied partto form the mold, which is then moved away from the model itself
using MoveFeatures.

6

MATERIAL EVALUATION

Objective. Before we test the effectiveness of ThermalRouter’ssolutions, we first characterize the materials employed by our tool.
To do so, we measured the relative thermal conductivities of eachmaterial.
Apparatus. To realize this, we built a hot-bed apparatus, depicted in Figure 12, using a Peltier element (CM23-1.9-05AC) andtwo temperature probes (100 kOhm NTC 3950). This apparatus
allows us to place a material sample in contact with the heating
element and measure how quickly the heat conducts through it.
This yields a proxy of the thermal conductivity of each sample. We
fabricated a 9.5 x 7.5 x 8 mm block of each material: PLA (in-plane& through-plane), silicone (Dragonskin FX pro), metallic-silicone(50 vol% EGaIn), and ICE9 Nylon (in-plane & through-plane).
Procedure. The Peltier was heated at constant voltage (2.6 V) for
7.5 minutes while measuring the temperature difference between
the Peltier surface and the top of the sample (two trials per sample,
averaged). Temperature difference started at 0°C as the experiment
began at room temperature (both faces were at the same temperature). Over time, a temperature difference arose corresponding to
the material’s conductivity as one face was heated.
Results. Figure 12 depicts our findings. We found that the basematerials, PLA, and silicone, have low thermal conductivities (i.e.,higher temperature difference in the plot, as they do not conduct
heat well through the sample), which validates their thermal issues.

Conversely, materials such as ICE9 Nylon and metallic-silicone,
have greater thermal conductivities (i.e., lower temperature difference in the plot, as they conduct heat better through the sample). This characterization validated the material assumptions uponwhich we later built our tool and tuned our simulations: simulating
the hot-bed apparatus gave temperature differences within 5%
for each material (note that Fusion 360 is limited to isotropic materials, thus our ICE9 material used the average thermal conductivityof the in-plane and through-plane conductivities).

7

ADDITIONAL EXEMPLARY USE CASES FOR
THERMALROUTER

After depicting ThermalRouter with the example of the handheld
game console, we now provide a broader illustration of its applicability. For each example object, we depict its baseline and the bestsolution generated and picked by ThermalRouter, alongside eachobject under our thermal camera.
Structural stability affected by heat sources: a 3D printed
lamp. In Figure 13, we show a 3D-printed lamp featuring a firebreathing dragon (a popular Thingiverse model [65]), with its 30W
incandescent bulb placed within the flame, giving it a glowing aura.
Unfortunately, after just 5 minutes, the heat produced by the bulb
causes the lamp’s plastic to melt and crumple under the dragon’s
weight. Instead, in the version generated by ThermalRouter, thechannels help to dissipate heat into the environment and provide
additional resistance to heat-induced deflection, allowing the lamp
to withstand high temperatures for longer than a 24-hour stress
test.
Precise geometric fits are affected by heat: a 3D printed
motor holder. In Figure 14, we depict a 3D printed fixture designed to hold a DC motor for a custom fan. Unfortunately, the heatbuildup as the motor spins causes the plastic to soften, undermining

UIST ’23, October 29–November 01, 2023, San Francisco, CA, USA

Alex Mazursky et al.

Figure 13: (a) A 3D printed lamp (lightbulb inside) features a dragon breathing fire; however, the heat generated by the lightbulb
causes plastic to deform and crumple under the weight of the dragon after just 5 minutes of being on. (b) ThermalRoutergenerates a solution that enables trapped heat to escape to the environment via heat channels, allowing the lamp to operate
without failures. By printing with black PLA, the channels can be concealed to preserve the lamp’s aesthetics.

Figure 14: (a) As the fan’s motor turns, its excess heat builds up at the fixture, causing the plastic to soften and loosen the fit. (b)ThermalRouter produces a solution that addresses excess heat by routing it away from the source via heat channels.

Figure 15: (a) A user notices that when gaming, their phone is warm to the touch because of its silicone case. (b) They use
ThermalRouter’s soft channels to let their case act as a heat sink that dissipates excess heat to the air, thus cooling down thephone.
the structural stability of the fit and causing the motor to dislodge
after just 7 minutes. Instead, the version made with ThermalRoutercan dissipate more heat away from the motor via conduction, thus
preventing plastic deformation. Moreover, in this example, ThermalRouter considered the user-defined speed of the fan’s air, allowing
it to use even less thermal material for a thermally-sound performance.

Soft objects also interact with heat sources: a silicone
phone cover. In Figure 15, we depict a situation where the soft heatchannels proved useful. The user custom-made a silicone sleeve
for their smartphone, which heats up at its center while gaming or
using GPS navigation. As depicted in Figure 15, ThermalRouter’s
soft heat channels route heat away from the hot spot, allowing theuser’s phone to feel less hot to the touch.

ThermalRouter: Enabling Users to Design Thermally-Sound Devices

UIST ’23, October 29–November 01, 2023, San Francisco, CA, USA

Figure 16: (a) A user makes a silicone sleeve for their ice pack. However, using silicone as a buffer insulates the user’s armfrom cooling down well. (b) A user instead uses ThermalRouter to generate soft heat channels that better distribute the coolsensation.
Cold can also be a thermal design goal: a wearable icepack. Figure 16 depicts a wearable patch designed to help the user
cool down their arm with an ice pack. For comfort, users typically
add a buffer between their skin and the ice pack (e.g., a towel).
Instead, this user uses ThermalRouter to design a silicone patchthat spreads out the cooling from the ice pack to a larger area. This
unique example makes use of ThermalRouter to route cold (via theabsence of heat at the pack creating a thermal gradient along thechannels). The thermal images in Figure 16 confirm that the ice
pack’s cold spot spreads more across the user’s skin after being
applied for 10 minutes.

8

CONCLUSION

In this paper, we presented ThermalRouter, an interactive design
tool that assists users with making thermally-sound devices. ThermalRouter embeds some of the required heat transfer domainknowledge directly into the CAD software, unlocking thermal
design for users. We designed ThermalRouter to tackle thermal
issues and confirmed the improved thermal performance of objects
created with this technique. Our approach covers a wide range ofuse cases, from traditional 3D printing to casting soft objects madefrom silicone. We hope this variety will foster creativity and use
by both researchers & maker community, who we tend to think assome of the prospective users of our tool.
For future work, we believe that researchers might extend ThermalRouter, which we made entirely open-source, by integrating
more advanced heuristics that generate more complex variations,or even more advanced algorithms to allow users to design for more
complex thermal situations.

ACKNOWLEDGMENTS
This work was partially supported by the University of Chicago Materials Research Science and Engineering Center, which is fundedby the National Science Foundation under award number DMR2011854. Moreover, we are grateful for the constructive feedback
from the reviewers.

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