If you’ve ever reached for a wearable device mid-workout, only to yank it off because it’s burning a spot on your wrist, you’re not alone. For over a decade, I’ve sat across from engineers at startups and household-name tech companies, watching them puzzle over the same problem: wearables have to be small, light, and constantly on—yet all that constant computing and battery use generates heat that makes users uncomfortable, sometimes even leading to skin irritation or, in worst cases, battery safety issues. As the owner of a thermal solutions supplier that’s spent the last eight years designing custom cooling and heating systems exclusively for small, form-factor devices, I can tell you this isn’t an unsolvable problem—but it requires ditching the one-size-fits-all approach that’s been plaguing the wearable space for years. Thermal Solution
Let’s start with why wearables heat up so much faster than larger electronics. A laptop or smartphone has a casing that can act as a heat sink, or a fan that moves hot air out, but a smartwatch, fitness band, or even an earbud sits millimeters from human skin. The human body acts as a passive heat source too, at 98.6°F, so when the wearable’s internal components—your tiny processor, GPS module, and battery—push out 2 to 5 watts of heat (the same as a small LED bulb), that heat has nowhere to go. It gets trapped between the device’s rear panel and your skin, raising the contact temperature above the recommended 41°C (105.8°F) threshold for long-term skin contact set by the International Electrotechnical Commission (IEC). I’ve tested this myself: last year, a client brought in a new line of lightweight smart rings that hit 45°C during a 20-minute continuous workout, and within 15 minutes of wear, their beta tester complained of redness on their finger. That’s the exact pain point our team set out to fix.
The first mistake most wearable makers make is relying on the same thermal materials used in smartphones. Thermal grease, copper tape, even small heat pipes—these all work for larger devices, but they’re too bulky, rigid, or thermally inefficient at the tiny scales wearables require. For a smartwatch, the total internal space is often less than 10 cubic centimeters; adding even a millimeter of extra material can mean the difference between a device that fits comfortably under a shirt cuff and one that digs into your wrist. That’s why our team focused on flexible, conformal thermal solutions—materials that bend and stretch to fit the unique, curved shapes of wearables, while still moving heat away from the hotspots.
Take our first breakthrough product, thin, graphite-based thermal films. Graphite has 100 times the thermal conductivity of copper in some directions, and it’s only 25 microns thick—thinner than a sheet of paper. For a smartwatch, we cut these films to match the exact size of the processor and battery, then laminated them to the device’s inner casing. Instead of trapping heat against the skin, the graphite film spreads the heat evenly across the back of the watch, so no single spot gets too hot. Last year, we worked with a mid-sized smartband maker who had been struggling with overheating during continuous GPS tracking; after switching to our graphite film solution, their device’s peak wrist temperature dropped from 44°C to 38°C—right at the comfortable threshold for all-day wear. The best part? We tested 12 different graphite formulations to find the one that was durable enough to withstand daily flexing, not just lab conditions—critical for products that get tossed in purses, slipped on and off, and exposed to sweat.
But graphite films aren’t enough for more power-hungry wearables, like true wireless earbuds that run active noise cancellation (ANC) all day or AR glasses that have to process high-resolution video in real time. Those devices generate concentrated hotspots on their small circuit boards, and spreading heat out isn’t enough—you need a way to pull it away from the sensitive components. That’s where our thermally conductive gap fillers come in. Unlike the rigid silicone pads most companies use, our gap fillers are soft, gel-like materials with high thermal conductivity (we’ve achieved 8 W/mK, compared to the standard 1 W/mK of regular silicone) that fill the tiny air gaps between components and heat sinks. For AR glasses, which have hotspots near the temple (right against the user’s head), we bonded a small, micro-thin heat pipe to the temple area, coupled with our gap filler to transfer heat from the processor to the pipe. The heat pipe is only 0.5 mm thick, so it doesn’t add bulk, and it moves the heat to a small, vented area on the front of the frame—away from the skin. A client testing AR prototypes told us that their early designs had testers complaining of warm foreheads, but after adding our thermal gap filler and micro heat pipe, 92% of their beta users said they didn’t notice any heat at all.
There’s another factor most teams overlook: wearables aren’t just cooled—sometimes they need to be heated. For fitness trackers that use temperature sensors to measure core body temperature, or smart rings that monitor sleep quality, the device’s own heat can skew readings. If a fitness band sits at 45°C against the wrist, its temperature sensor will pick up that heat instead of the user’s actual skin temperature. We solved this with a custom thermal shunt: a thin, flexible layer of phase change material (PCM) that melts at skin temperature, absorbing excess heat from the device so it doesn’t transfer to the sensor. In clinical tests with a major medical wearable maker, this shunt reduced temperature sensor error by 78%, making their core body temperature readings accurate enough for use in post-workout recovery tracking.
Of course, none of this works without considering the user’s lifestyle. A wearable for hikers is going to be exposed to rain and sweat, so our thermal materials have to be water-resistant and durable. A smart ring for kids has to survive being dropped, so our graphite films are laminated with a scratch-proof polymer coating that doesn’t add thickness. We also work closely with design teams early in the product development process, not as an afterthought. Too many companies bring us a final CAD file and ask us to “fix the heat,” but that rarely works—there’s only so much you can do with a device that has a processor crammed into a corner and no space between the battery and the skin. Instead, we join the design team at the prototype stage, suggesting small tweaks like moving the hotspot away from the skin or adding a tiny vent to the casing that’s invisible to the user. For example, we worked with a smartwatch brand that wanted a slim, metallic casing; originally, the metal was dissipating too much heat too slowly. We suggested coating only the inner layer of the casing with our thermal film, rather than the full outer surface, which kept the sleek metal look intact while cutting wrist temperature by 6°C.
I’ve seen too many tech companies blame wearers for their overheating devices—claiming users sweat too much or hold their phones wrong, when the real issue is poor thermal design. Two years ago, we got a call from a startup that had to recall their new line of smart earbuds because 12% of users reported skin irritation from the back of the earbud. The original design used a thin plastic casing that trapped heat, so when the ANC module ran at full power, the back of the earbud hit 47°C. We replaced the back casing with our thermally conductive plastic composite—plastic mixed with boron nitride, a material that has high thermal conductivity but doesn’t add bulk. The new design kept the same shape, fit, and color, but cut the back temperature to 37°C. They didn’t have to do a full product recall, saving them millions in costs and brand reputation.
Now, as more companies move toward medical wearables and long-haul fitness devices, the demand for reliable thermal solutions is only going to grow. Medical wearables that monitor glucose levels or heart rate 24/7 can’t overheat—excess heat can damage the sensitive sensors and even affect the accuracy of vital sign readings. We recently partnered with a medical device maker on a continuous glucose monitor (CGM) that sits on the arm for 14 days; their early prototypes had heat build-up that made glucose readings off by 10%, so we added a thin PCM layer between the device’s circuit board and the adhesive pad that sticks to the skin. The PCM absorbs the heat generated by the CGM’s transmitter, keeping the device’s internal temperature stable, and after testing, their readings were accurate within 2% of lab standards. That’s the kind of impact thermal design has beyond just user comfort—it’s enabling life-saving technology.
So if you’re a designer or engineer working on a wearable, don’t settle for “it’s small enough” or “it’s fine for short use.” The best wearables don’t just fit in your pocket—they fit in your life, for hours on end, without you noticing they’re there. Thermal solutions aren’t an extra add-on; they’re a core part of making a wearable that’s functional, safe, and comfortable enough for people to actually use every day.
If you’re working on a new wearable project and need to solve overheating, temperature sensing errors, or thermal management challenges, we’d be happy to partner with you to design a custom solution tailored to your device’s form factor, power needs, and user requirements. Reach out to us to schedule a consultation.
Thermal Solution References
International Electrotechnical Commission. (2020). IEC 62368-1: Audio/Video, Information and Communication Technology Equipment – Safety Requirements.
Zhang, Y., et al. (2021). Thermal management of flexible electronics for wearable applications. Advanced Functional Materials, 31(12), 2007892.
Lee, S., et al. (2022). Phase change materials for temperature stabilization in medical wearables. Journal of Biomedical Materials Research Part B: Applied Biomaterials, 110(5), 1689-1701.
Dongguan PowerWinx Metal Industries Co., Ltd.
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