Copper prices tumbled but the materials sector actually rose. Why did they move so differently within the same commodity-related category?

Scenario Divergence: How a Tariff Delay Split Copper From the Materials Sector

Today copper fell -2.86%, but the materials sector ETF XLB actually rose +0.48%. The reason for this split within the same "materials" category is that tariff-policy uncertainty acted narrowly on copper alone.

What Happened

In the second week of September, a Reuters report that the White House had put its decision on tariffs for imported refined copper on hold triggered a nearly 5% plunge in copper prices, ending a 10-week streak of weekly gains that had run since June (Rio Times/Business Recorder, 2026-09). Just before that, COMEX copper had hit a record $14,875 per ton, reflecting expectations that tariffs would push U.S. copper prices even higher — expectations that had already been priced in. The White House reportedly held off on tariffs due to concerns about manufacturer inflation ahead of the midterm elections and the risk that tariffs could push domestic copper prices even higher (Rio Times, 2026-09). In the wake of this, Freeport-McMoRan fell -8%, and Teck Resources and Southern Copper each dropped -7% (Yahoo Finance, 2026).

Why Didn't XLB Fall Along With It

XLB isn't an ETF holding only copper miners. It's diversified across chemicals, steel, gold mining, and packaging, so news confined to a single metal like copper tariffs often stays contained to specific stock groups rather than dragging down the whole index. Today, directions diverged even within the materials sector's sub-components — silver rose(+0.93%) while gold slipped slightly(-0.43%). It's more accurate to read XLB's +0.48% not as "the whole materials sector is strong" but as "copper weakness was offset by other sub-components."

The Tariff Decision, the Next Inflection Point

The tariff issue itself isn't resolved. The 50% tariff on semi-finished copper and 25% on derivative products that took effect in April remain in place, and a plan is under discussion to introduce a 15% tariff on refined copper starting in 2027, stepping up to 30% by 2028 (Argus Media/Recycling Today, 2026). Goldman Sachs expects copper prices to actually fall once tariff uncertainty is resolved, given an expected supply surplus of 262,000 tons in 2026 and over 700,000 tons annually in 2027-28 (Goldman Sachs, 2026). In other words, neither confirming nor scrapping the tariff is a bullish catalyst for copper.

So What Should Investors Do

Just because XLB held up doesn't mean individual copper miners like Freeport-McMoRan are equally safe. Individual copper mining stocks are sensitive enough to policy headlines that a single delayed-decision report can trigger a 7-8% drop, and combined with Goldman Sachs' supply-surplus outlook, the risk is structurally skewed to the downside rather than the upside. For materials exposure, a diversified ETF like XLB is a safer way to reduce policy-headline risk than a single copper-mining stock, and it's prudent to hold off on new positions in individual copper miners until a final tariff decision is made.