McNICHOLS Expanded Metal: Raised or Flattened, and Which Alloy

Does it actually matter whether I order raised or flattened expanded metal, or is it just a look? It matters. Flattening cold-rolls the strands and cuts the panel's overall thickness roughly in half, so the two patterns behave differently the moment they go on a job. The pattern decides most work, not the alloy.

I keep two 24 by 24 in. panels of the same spec in the shop — 3/4 in. no. 9 carbon steel, one standard raised and one flattened. I've run a palm across both, put a caliper on both, and loaded both. My answer comes from those two panels plus what McNICHOLS prints about how expanded metal is made and what it gets sold for.

Pick Raised or Flattened by the Job

On a job site the question is never abstract. A maintenance tech ordering a machine guard, a contractor closing off a window, a fabricator building a shelf — each one needs the pattern that matches contact and drainage, not the one that photographs better.

I ran my palm across the two panels side by side. The raised one catches skin on the high points of the diamond; the flattened one slides under my hand and doesn't scrape. That's the whole difference in one gesture, and it's why flattened gets specified wherever people or parts slide across the surface.

McNICHOLS supplies the line in a Standard (Raised) diamond pattern and a Flattened variety, so the choice is made on the order form, not at the loading dock. On the same pattern designation, only the surface changes between them.

My rule: need grip, drainage, or resistance to foot traffic, order raised. Need a flat, thin surface that sits against a frame or a face — shelving, signage, guards, ceiling tile — order flattened. If you're standing on it, raised. If you're looking at it or sliding something over it, flattened.

What Slitting and Stretching Does to a Sheet

McNICHOLS expanded metal starts as a solid sheet that gets slit and stretched to open diamond-shaped holes. No material is punched out and hauled to the scrap bin. The slits are staggered row to row, and when the sheet is pulled, the metal between them rolls into strands and the diamonds open up.

That's why the scrap bin stays empty on this product. A perforated panel wastes the punched slugs; expanded metal keeps every ounce of the original sheet and just rearranges it. Strands and holes are the same metal, pulled apart rather than cut away.

Stretching is cold work, and cold work does something to the steel. Dislocations multiply, yield strength climbs, and the sheet picks up a temper it never had flat. There's a trade built in, though: pull a longer pattern or run a narrower strand and the load-bearing metal per square foot shrinks. Longer diamond, less stiffness. That trade lives in the pattern designation, which is why I don't swap patterns on a load-bearing panel without checking the numbers.

What My Caliper Found on Two Panels

I measured overall thickness at three spots on each panel and averaged. The raised panel came in around 0.25 in.; the flattened panel measured about 0.13 in., roughly half, which is what a pass through the rolls should do. Strand thickness barely moves. The panel's overall height collapses when the strands get pressed down.

Weight per square foot was identical between the two. That tripped up a fabricator I worked with last spring — he assumed flattened had to be lighter because it's thinner. It isn't. Flattening doesn't remove metal, it reorients it, so the scale reads the same on both.

Then I set a 20 lb. weight at mid-span on a 24 in. span of each. The raised panel sagged slightly less than the flattened one. The angled strands give raised more section depth, and depth beats weight when you're bending a panel. Flattened is flatter, not stiffer.

When I'd Flip My Own Recommendation

Raised wins by default, but a handful of conditions flip the choice the other way.

Welding or face-mounting: flattened lies flat against a frame and welds along a continuous edge. Raised, compared with flattened, only touches at the peaks of the diamond, so you get point contact and a gap the panel can rock against. If the panel has to sit flush, flattened.

Rolling or sliding loads — cart wheels, a skateboard, a drawer slide — ride up on the raised strands and hammer them flat. Flattened takes that load on a level plane. If it rolls, flattened.

The reverse is just as firm. Anti-slip walkways, drainage grates, ventilation openings, raised. Flattened kills the drainage and the bite in one pass through the rolls.

Salt air or chlorides flip the whole decision up a level. There the material decides survival before the pattern matters — switch to 316 stainless first, then argue raised against flattened with what's left. And if you came in believing flattened is a pressed-down raised that must be stronger because it's denser, that's the belief my recommendation overturns. Flattened is a cold-rolled product, not a compressed one.

Which Alloy Survives Your Service Environment

McNICHOLS runs this line in aluminum, carbon steel, galvanized steel, and stainless steel. The diamond doesn't change how any of them corrode. The alloy does.

Aluminum builds its own oxide skin within minutes and repairs it when scratched. It runs about a third the density of steel, which is why it shows up on ceilings and signage. Carbon steel is the cheapest of the four and the one that rusts. Coat it or watch it go, and a cut edge in carbon steel is bare metal that starts bleeding rust.

Galvanized steel carries a zinc coating that works as a sacrificial anode. Scratch through to the steel and the zinc around the scratch still protects it. That's why galvanized holds up outdoors on a budget, though the surface will bloom white rust in wet, trapped conditions where air can't move.

Stainless leans on a chromium-rich passive film. Type 304 handles most weather. Type 316 adds molybdenum and holds up where chlorides pit straight through 304 — coastal air, road salt, a wash-down with chlorinated cleaner. Pick the material by what the panel will see, then pick the pattern.

Screens, Guards, and Ceiling Tile Need Different Panels

The line covers screens, window security panels, and machine guards, with the decorative stock turning up in shelving, signage, and ceiling tile. Those uses pull the choice in different directions.

A machine guard is a safety part, so opening size leads. The opening has to be small enough that a finger or a flying chip can't pass, which puts you in a small pattern. Carbon or galvanized is enough indoors; galvanized if coolant and wash-down are in the picture.

Window security panels want raised, small opening, and stainless. Raised because the angled strands present an edge to a blade, and stainless because a storefront window sees weather and cleaning chemicals.

Shelving, signage, and ceiling tile go the other direction: flattened, and usually aluminum. Flat because the panel meets a frame or a face, aluminum because a ceiling panel and a sign need to stay light. Unlike a raised panel, a flattened one sits down in a T-bar grid instead of throwing shadows from every peak.

How I'd Check a Panel in Ten Minutes

Before a full order ships, ten minutes at the bench tells me whether the lot is what I asked for.

First, caliper the overall thickness in three spots. That confirms raised against flattened on the spot, and it flags a panel that rolled out of spec — thickness outside the pattern's range is a return, not a discussion.

Second, drag a palm across the face. Flattened shouldn't scrape; raised should bite. If a flattened panel bites, it wasn't flattened, and it will tear up anything that slides over it.

Third, water and air. Pour a cup across both and watch where it goes, then blow air through and feel it on the far side. Raised drains and vents better than flattened on the same pattern, and if the job is a drain grate or a vent, that test is the whole spec.

Fourth, grab a corner and flex it by hand. That tells me how hard the sheet was worked before it reached me — the temper. A panel that flexes like a noodle won't hold what the pattern sheet promises. Each check maps to a reason to send the lot back, so I'm not betting a whole order on the first panel I touch.

The question I get most: if flattening presses the strands down, doesn't it rob strength? It doesn't. Flattening lowers the panel's height, not its cross-section — load still follows strand width and pitch, so a flattened panel is no weaker than a raised one of the same designation. What you give up is the bite and the drainage channel. Decide with one question: will anything or anyone travel across this face? If yes, keep the raised diamond, or change the material before you change the pattern.