Hey everyone, it’s Jake here, from the team that makes those shaped copper capillary tubes you might’ve heard about. Lately, I’ve been getting so many DMs and emails asking the same question: “What’s the actual thermal conductivity of your shaped copper capillaries? I keep seeing basic copper numbers online, but that doesn’t feel right for the bent or flared or custom-shaped stuff you sell.” Fair question—most people don’t stop to think that shaping copper isn’t just reshaping metal, it messes with how heat moves through it, and that’s exactly what we’re here to break down today. Let’s skip the boring textbook jargon, keep this real, and answer this once and for all. Shaped Copper Capillary Tube
First, let’s start with the basics. Everyone knows plain, straight, annealed copper has a thermal conductivity right around 401 W/m·K at room temperature, right? That’s the number you’ll see everywhere, from your high school physics textbook to random product spec sheets. But here’s the thing: that’s for a perfect, unformed piece of copper—no bends, no custom shaping, no thickness changes along the length. Shaped copper capillaries? We’re not just cutting a straight tube to length. We do all kinds of shaping—flaring the ends for fittings, bending tight 90-degree angles for HVAC coils, flattening sections for compact electronic cooling, even making custom oval or square cross-sections for tight spaces. Each of these steps changes the thermal conductivity, sometimes in big ways, sometimes small, depending on what you’re using it for.
Let’s talk about what actually affects thermal conductivity in shaped tubes. The main one here is deformation. When you bend copper, or work-harden it, that’s where things shift. Copper is a ductile metal, so when you bend it, pull it, or hammer it into a new shape, you’re rearranging the crystal structure of the metal inside. That rearranged structure makes it harder for electrons (the things that carry heat through metals) to move smoothly, which drops thermal conductivity a little. For most of the shapes we make—like gentle bends, which are super common in refrigeration lines—this drop is tiny, like less than 2% from the 401 W/m·K baseline. If you have a tighter bend, like a 180-degree bend with a really small radius, you might see a drop of 3-5%, still not enough to stress about for most applications.
Wait, but what if we’re talking about flared ends? Flaring is when we widen the end of the copper capillary to connect to a fitting, right? We do that by heating a small section and forming it with a die. That area stays annealed (soft, unworked) so it doesn’t crack, and annealing actually brings conductivity up a tiny bit—sometimes to 403 W/m·K, barely higher than base copper. So that flared end? It’s not a weak spot for heat transfer, that’s good news.
What about the other shapes we make, like flattened capillaries for LED coolers or automotive parts? Flattening a capillary is a bit more intense, especially if we’re reducing its cross-section by more than half. In that case, work hardening is more noticeable, so thermal conductivity drops a bit more—usually around 7-10% from the baseline, so around 360-370 W/m·K. But even that? It’s still way higher than other common materials people use for these applications, like aluminum (which is around 205 W/m·K) or even some plastics, so you’re still getting way better heat transfer than you would with alternatives.
Now, let’s get to the stuff people actually care about: when does this conductivity change matter, and when is it no big deal? Let’s split this into common use cases, since that’s what our customers care about. First, HVAC and refrigeration lines—this is our biggest market for shaped copper capillaries. Most HVAC systems use bent copper capillaries to carry refrigerant between the evaporator and condenser. For these, the average thermal conductivity across the entire bent length is almost always within 95% of the baseline, because the bends are gentle, and any flattened sections there are super minimal. So if you’re replacing a straight copper capillary with a bent shaped one, you won’t notice a difference in cooling efficiency at all. We’ve tested this with a local HVAC company last year—they ran side-by-side tests of straight vs our 90-degree bent capillaries on a 2-ton unit, and the cooling COP (Coefficient of Performance) was identical within margin of error. That’s proof right there.
Next, electronic cooling—this is a growing area for us, with people using shaped copper capillaries to cool high-power LEDs, server chips, and electric vehicle batteries. Here, shape matters because you need the heat pipe or capillary to fit into tight spaces, so flattening or shaping into irregular cross-sections is common. For these applications, the 7-10% conductivity drop I mentioned earlier? It’s still not a problem. Let’s do a quick math check: base copper is 401, shaped flattened is ~370. That’s still almost double aluminum, so even with that drop, it’s transferring heat way faster than aluminum would. We work with a server manufacturer that uses our custom shaped copper capillaries for their CPU coolers, and they told us that switching from aluminum to our shaped copper capillaries cut their CPU temperatures by 12 degrees, even with the small conductivity drop from shaping. So the shape’s ability to fit and make contact with the hot surface is way more impactful than the tiny conductivity change.
Wait, but what about when people say “shaped copper capillary” and mean something way more extreme, like twisted capillaries or ones with welded sections? Yeah, those are less common, and they do have a bigger conductivity hit. Twisted copper capillaries, for example, work harden a lot along the twist, so conductivity can drop 15-20% in the twisted section, around 320-340 W/m·K. But unless you’re making something for a specialized lab or aerospace application, twisted capillaries aren’t something our standard line offers—we only make shapes that are optimized for heat transfer, not just weird form factors. Welded sections? We only weld copper to copper for our capillaries, and we use fusion welding that doesn’t mess with the crystal structure too much, so the conductivity in the weld zone is still around 90% of baseline, same as bent sections.
A lot of people also ask if size matters, right? Capillaries are tiny, usually 0.5mm to 6mm outer diameter. Does the size of the tube affect thermal conductivity, even when shaped? Honestly, not really—unless you’re going below 1mm outer diameter. For those super tiny capillaries (like 0.5mm OD), the surface area to volume ratio goes up, and surface oxidation (which happens when we heat and shape the tube) can have a tiny effect. But even then, the drop is less than 5%, so it’s negligible for almost any use case. We test every batch of our 0.5mm shaped capillaries, and their thermal conductivity is still around 380 W/m·K, which is way better than any other material for that size.
Let’s also talk about how we test this, because numbers mean nothing if you just pull them out of thin air. We don’t just take the base copper number and adjust for shape—we do actual thermal conductivity tests on every shaped batch we make. We use a standard transient hot wire method, which is the same method used by labs and material testing companies. For every shape: bent, flared, flattened, we take samples straight off the production line, cut them to test length, and run the test at room temperature (25°C, which is standard for these tests). Our average results across all our standard shaped capillaries:
- Gentle bends (radius > 5x tube OD): 390-400 W/m·K
- Tighter bends (radius 2-5x OD): 375-390 W/m·K
- Flared ends: 400-405 W/m·K
- Flattened capillaries (cross-section reduced by 30-50%): 355-370 W/m·K
- All shapes combined average: ~385 W/m·K
That average is way more useful than the base 401 number, because that’s what our customers are actually using. Most of the time, when you look at spec sheets for “shaped copper capillaries,” they just list the straight copper number, which is misleading. We don’t do that—we list our actual tested numbers on every product page, so you know exactly what you’re getting.
Now, let’s clear up a common myth: people think that because the tube is shaped, there’s more surface area, so heat transfer is better regardless of conductivity. That’s partly true, but it’s not the only factor. Conductivity still matters for the actual movement of heat through the metal. For example, if you have two capillaries with the same shape, one is shaped copper with 385 W/m·K, the other is shaped aluminum with 205 W/m·K, the copper one will transfer more heat every time, even if the shape is identical. The shaping helps, but the metal itself is still the bigger driver.
Wait, what about high temperature applications? Like, if you’re using these capillaries in a furnace or a high-heat industrial process, does the conductivity change more when shaped? Let’s test that. At 100°C, base copper conductivity drops to around 390 W/m·K, right? For our shaped capillaries, the drop is about the same—so a bent capillary that’s 385 W/m·K at room temp is 375 W/m·K at 100°C, which is still in line. At 200°C, base copper is 375 W/m·K, our shaped ones are around 350 W/m·K, so the difference stays consistent. Even at 500°C, where copper’s conductivity is around 300 W/m·K, our shaped ones are still around 280 W/m·K, so the percentage drop from baseline stays almost the same across temperatures. That’s good news for anyone using these in high-heat settings, like industrial heat exchangers.
I’ve been in this business for 8 years now, and the number one mistake I see customers make is taking the base copper thermal conductivity number and applying it directly to shaped capillaries. It’s not wrong, it’s just not accurate enough. If you’re designing a new HVAC system, or a CPU cooler, or a refrigeration unit, that 10-15% difference between base copper and actual shaped copper could mean the difference between a unit that runs too hot and one that works as intended. That’s why we always tell our customers: if you have a design that relies on precise heat transfer numbers, send us your specs, and we’ll test custom shaped samples for you, with their exact conductivity. We don’t want you to guess—we want you to have real, tested numbers.
Another thing people ask: does plating affect it? A lot of customers ask if we plate our shaped copper capillaries with nickel or tin for corrosion resistance, and how that affects thermal conductivity. Plating is a thin layer (usually 0.001mm to 0.005mm) so it barely affects the overall conductivity. Even if we plate the entire tube, the copper underneath is still doing 99% of the heat transfer, so the total conductivity drops by less than 1%. That’s nothing, so plating for corrosion is totally worth it, no heat tradeoff.
Let’s wrap this up, because I know we covered a lot. To answer the original question: the thermal conductivity of shaped copper capillary tubes isn’t a single number. It depends on the type of shaping, how extreme the shape is, the size of the tube, and the temperature it’s used at. For our standard shaped copper capillaries (the ones we make most often for HVAC, electronics, industrial use), you can expect an average conductivity of ~385 W/m·K at room temp, ranging from ~355 W/m·K for heavily flattened sections to ~400 W/m·K for gentle bends or flared ends. That’s still way higher than any common alternative materials, and the shape of the tube usually improves heat transfer way more than the tiny drop in conductivity from shaping.
If you’re working on a project where this actually matters—like a high-efficiency refrigeration system, a compact EV battery cooler, or a high-power LED array—don’t just go with a generic copper number. Reach out to our team, tell us what shape you need, what size, what temperature you’ll be working at, and we’ll hook you up with tested samples and exact conductivity data tailored to your needs. We don’t do one-size-fits-all here, and we’re happy to answer any more questions you have, not just about thermal conductivity, but about anything related to shaped copper capillaries. We’ve been doing this long enough to know that the small details (like this conductivity thing) are what make or break a project, and we’re here to make sure you get the right product for your job.
Don’t hesitate to hit us up if you need anything—whether it’s a sample, a spec sheet, or just another answer to that question you can’t find online. That’s what we’re here for.
Shouldered Copper Capillary Tube References
- Ho, C. Y., Powell, R. W., & Liley, P. E. (1974). Thermal conductivity of the elements. Journal of Physical and Chemical Reference Data, 3(1), 1-79.
- Taylor, D. (1989). Work hardening of copper and its alloys. Materials Science and Technology, 5(10), 954-962.
- ASHRAE Handbook: Refrigeration. (2022). American Society of Heating, Refrigerating and Air-Conditioning Engineers.
- Mills, A. F. (2001). Heat Transfer (2nd ed.). Prentice Hall.
- Our in-house production and testing data, 2016-2024.
Xinchang Sancai Machinery Co., Ltd.
As one of the most professional shaped copper capillary tube enterprises in China, we’re featured by quality products and good price. Please rest assured to buy durable shaped copper capillary tube made in China here from our factory. We also accept customized orders.
Address: Building No.3, 1# Xinying Road, Xinchang County, Zhejiang, China
E-mail: scjxoverseas@126.com
WebSite: https://www.sccooltube.com/
