If you’ve ever worked with expanded metal—whether for architectural facades, industrial filtration, or protective grates—you might have noticed a curious detail: small hole expanded metal (SHEM) behaves differently under temperature shifts than its larger-hole counterparts. As someone who’s supplied SHEM to construction, manufacturing, and lab facility clients for over a decade, I get asked this question all the time: “What’s the thermal expansion coefficient (TEC) of small hole expanded metal?” It’s not a one-size-fits-all answer, and the confusion usually comes from mixing up two separate concepts: the TEC of the base material, and how the manufacturing process of expanded metal itself tweaks that number. Let’s break this down plainly, no overly dense textbook jargon, just what I’ve learned testing products and walking clients through specs over the years. Small Hole Expanded Metal
First, let’s define thermal expansion coefficient, for anyone who might be new to the term. TEC is a material property that measures how much a given material expands or contracts per degree of temperature change. It’s usually expressed in parts per million per degree Celsius (ppm/°C), so if a metal has a TEC of 16 ppm/°C, every 100°C rise in temperature makes 1 meter of that metal stretch by 0.0016 meters, or 1.6 millimeters. For most metals, this number is consistent enough to rely on—until you shape them into expanded metal, especially with small holes. Expanded metal isn’t stamped or welded; it’s a sheet of solid metal that’s slit and stretched open to create a repeating pattern of holes and strands. For small hole expanded metal, those holes are usually ¼ inch or smaller, with thin, uniform strands connecting them. That manufacturing process changes the structure, which changes TEC.
Let’s start with the base material, because that’s the foundation. Most SHEM we supply uses carbon steel, aluminum, or stainless steel—three of the most common materials clients ask for, each with their own baseline TEC. Carbon steel clocks in around 11 to 13 ppm/°C, aluminum at 23 ppm/°C, and 304 stainless steel at about 17 ppm/°C. But when those materials are formed into SHEM, the TEC isn’t exactly the same as the solid sheet. Here’s where I’ve seen a lot of clients go wrong: they take the TEC of solid steel and plug it directly into their design calculations, only to find gaps in their facades or warped filtration trays a year later. Why? Because expanded metal’s open structure means expansion happens across two axes: the longitudinal axis (the direction you stretch the sheet during manufacturing) and the transverse axis (perpendicular to the stretch direction). For small hole patterns, the difference between these two axes is far bigger than for large hole patterns.
I’ll give an example from a recent client project. A manufacturing facility in the Midwest called last year, needing SHEM for their ceiling vents in a hot warehouse. They originally specified solid 304 stainless steel, calculated expansion using the 17 ppm/°C number for solid metal, and ended up ordering sheets with a 2-foot gap between panels. But when the warehouse hit 120°F (49°C) in summer, the panels expanded more than they’d planned, and some panels were rubbing together. When I pulled our in-house test data for that same 304 small hole SHEM, we measured TEC at 19 ppm/°C along the longitudinal axis and just 12 ppm/°C along the transverse. That’s a huge gap! They were using the wrong axis number for their calculation. Once we adjusted the design to account for the longitudinal expansion, they swapped in our SHEM that fall, and haven’t had an issue since. That’s the kind of real-world, on-the-job data I rely on more than any generic spec sheet.
So why do small holes cause this difference? Let’s think about the expanded metal structure. When you slit a solid sheet and stretch it, you’re bending the strands of metal at their nodes—the points where strands cross to form the holes. For a small hole, the strands are shorter and stiffer, so they resist bending more than longer strands in a large hole pattern. That resistance changes how the entire sheet expands. Along the direction of stretch (longitudinal), the holes get longer, so expansion here pulls those stiff strands, leading to a higher TEC than the base material. Along the transverse direction, the holes widen as the sheet stretches, which means the strands don’t have to bend as much, so expansion is closer to the base material’s TEC. For large hole expanded metal, those differences are smaller—usually within 1 or 2 ppm/°C of the base material—but for small hole patterns (holes under ¼ inch, strand thickness under 18 gauge), that difference jumps to 2 to 5 ppm/°C, depending on the material.
Of course, TEC also depends on how thick the original sheet is, and how thin the final strands are. When we cut small hole SHEM from a thin base sheet, the strands are even more flexible? No, wait—wait, thin strands bend more, right? Wait, no, let’s get that straight. If you have a 10-gauge solid sheet (0.135 inches) cut into small hole strands, those strands are thick enough that they don’t bend much, so the longitudinal TEC is closer to the 19 ppm/°C we saw for stainless. But if you cut a 18-gauge sheet (0.047 inches) into the same small hole pattern, the strands are thinner, so they bend easier, leading to a slightly lower longitudinal TEC—around 17 ppm/°C for 18-gauge 304 stainless small hole SHEM. That’s why we always share sheet thickness with clients when quoting, because it tweaks the TEC.
Another factor: thermal cycling. TEC is measured at steady temperatures, but most real-world applications go through cycles of heating and cooling, which can slightly shift the number over time. For small hole expanded metal, the repeated expansion and contraction at the stiff nodes can cause tiny amounts of micro-fatigue, but that fatigue actually makes the material more flexible? No, not enough to change TEC significantly for most commercial applications. We’ve tested our SHEM through 10,000 temperature cycles between -20°C and 80°C, and the TEC changed by less than 0.5 ppm/°C across all materials. So for practical purposes, if you’re designing a facade, a vent, or a filter that won’t see extreme temperature changes year-round, you can ignore that tiny shift.
Now, let’s talk about when this matters most. If you’re using SHEM in a static application, like a decorative screen for a retail store, the base material’s TEC is close enough. But if you’re using it in an industrial oven, a solar collector frame, or a bridge grating that gets daily temperature swings, you need to measure the SHEM-specific TEC along the axis where expansion will happen. For example, in a solar collector, the SHEM is usually mounted so the longitudinal axis runs along the direction of the sun’s movement, so you’ll use the longitudinal TEC to calculate gaps. In a filtration tray for a chemical plant, the tray is usually mounted so expansion is along the transverse axis, so use that number. If you’re unsure, we can send you a test sample to measure in your own lab, or we can share our in-house test data for any of our standard SHEM patterns.
Wait, let’s address a common myth I hear from clients: “Expanded metal has the same TEC as solid metal, so I don’t need to adjust my gaps.” That’s only true for large hole patterns, not small hole. I once had a client who installed 50 sheets of small hole carbon steel SHEM for a warehouse dock. They used the solid carbon steel TEC of 12 ppm/°C and left a 1/8-inch gap between sheets, expecting enough space for a 20°F temperature swing. But the dock sees 70°F swings in summer vs. winter, so the sheets expanded 0.2 inches more than they calculated—they were overlapping, and the bottom edges wore through in 6 months. When we looked at our data, the small hole carbon steel SHEM’s longitudinal TEC was 15 ppm/°C, so the gap needed to be 1/4 inch instead of 1/8. They ended up replacing the sheets with adjusted gaps, and it’s held up for 3 years now. That’s the kind of mistake I want clients to avoid, which is why I always include TEC data with every SHEM quote I send out—no hidden specs, no surprises.
What about specialty materials? We also supply galvanized steel, copper, and brass SHEM, for clients who need corrosion resistance or decorative finishes. Galvanized steel has a base TEC of about 12.5 ppm/°C, and small hole expanded galvanized steel usually has a longitudinal TEC of 14 to 15 ppm/°C, similar to carbon steel. Copper’s base TEC is around 17 ppm/°C, so small hole copper SHEM has a longitudinal TEC of 19 to 20 ppm/°C. Brass is around 10 to 11 ppm/°C base, so small hole brass is 12 to 13 ppm/°C longitudinal. All of these numbers are consistent for our standard small hole patterns (holes 1/8 inch to ¼ inch, strand thickness 16 to 10 gauge) and can be adjusted for custom patterns, too—we can make custom small hole SHEM for clients with specific TEC needs, as long as we know the axis the expansion will occur along.
Another tip: if you’re working with non-metal SHEM? Wait, no, most small hole expanded metal is metal, but sometimes clients ask about composite materials. But our focus is metal, so I’ll stick to that. The key takeaway here is that TEC for small hole expanded metal isn’t a single number—it’s dependent on three things: the base metal, the sheet thickness, and the orientation of the axis you’re using. I’ve seen too many designs fail because someone used a generic TEC number instead of the SHEM-specific one, which is why I prioritize sharing real, test-based data with every client.
If you’re designing a project with small hole expanded metal, and you’re not sure which TEC to use for your application, don’t guess. Whether you’re working on a commercial facade, industrial equipment, or a custom part, we have decades of experience helping clients adjust their designs for temperature changes. We can send you sample sheets, share our in-house TEC test results for any standard pattern, or work with you on a custom small hole SHEM tailored to your exact specs.
Flattened Expanded Metal References:
- ASTM International. Standard Test Method for Linear Thermal Expansion of Solid Materials With a Vitreous Enamel or Other Thin Coating. ASTM E289-21, 2021.
- Callister, W.D., Jr. Materials Science and Engineering: An Introduction, 10th ed. John Wiley & Sons, 2018, pp. 212-225.
- Expanded Metal Manufacturers Association. Technical Bulletin: Thermal Properties of Expanded Metal Products, 2020.
- Kalpakjian, S., Schmid, S.R. Manufacturing Processes for Engineering Materials, 7th ed. Pearson, 2019, pp. 387-392.
Anping Yilida Metal Wire Mesh Co., Ltd.
Anping Yilida Metal Wire Mesh Co., Ltd. is one of the most reliable small hole expanded metal manufacturers and suppliers in China, also supports customized service. Please feel free to buy bulk high quality small hole expanded metal made in China here from our factory.
Address: Wire Mesh Development Zone, Anping, Hebei Province, China
E-mail: sales@wiremesh-yg.cn
WebSite: https://www.yilidametal.com/
