May's Producer Price Index shows flat glass costs easing for the second time in three months while fabricated metal and architectural metalwork keep climbing—and processed energy prices are up 43.6% year over year. For glaziers, GCs, and spec writers chasing escalation clauses, the divergence is reshaping how envelope packages get priced.
A Two-Speed Cost Environment Inside the Same Bid Package
The Bureau of Labor Statistics' May 2026 Producer Price Index, released last week, delivered a result that should change how envelope contractors think about escalation: glass got cheaper, metal got more expensive, and energy went vertical. For anyone pricing a curtain wall, window wall, or storefront package right now, that divergence is the story.
The price of glass products and the cost to manufacture them fell for the second time in three months, with glass and glass product manufacturing dropping by 0.2% in May and sitting 5.3% higher than in May 2025. The PPI tracks the average change in selling prices received by domestic flat glass, container and pressed/blown glass manufacturers.
On the flat glass side specifically, the cost of flat glass dropped in May, falling by 0.1% after April's 0.2% increase. Despite the drop, flat glass prices were still up 6.1% compared to May 2025. The price to manufacture flat glass dropped as well, declining by 0.2% following a 0.5% increase in April. On a year-to-year basis, the cost of manufacturing flat glass was up 6.6%.
That's the good news. The bad news is what's happening on the metal line items.
Aluminum and Steel Keep Climbing
The cost to fabricate structural metal products jumped in May, the fourth consecutive month that prices for the index have risen by nearly or more than 1% in a given month. BLS reports that fabricated structural metal product prices rose by 1.1% last month and sit 8.1% higher than in May 2025.
For architectural envelope work, the more relevant index tells the same story. Ornamental and architectural metalwork prices climbed for the fourth straight month in May, rising by 0.8%. That's the category that captures aluminum extrusions, formed metal panels, sunshades, and decorative trim—the bones of every curtain wall and storefront system on a commercial job.
This isn't a one-month blip. While the cost of flat glass products and their manufacturing dropped this past month, the same cannot be said for metal products associated with architectural glass. BLS data indicates that metal used to fabricate window systems rose by 1% in some cases.
The Energy Wildcard
The number that should worry every envelope manufacturer planning Q3 production is buried in the energy line. Per May's PPI, processed energy goods rose by 10.4% and sit 43.6% higher than in May 2025.
That matters because the float glass furnace is one of the most energy-intensive pieces of equipment in the building products supply chain. The May glass price drop almost certainly reflects softer demand and inventory rebalancing rather than easing input costs. If energy stays where it is, the next two PPI prints are unlikely to repeat the dip.
It also sets the macro backdrop: the overall PPI for final demand rose by 1.1% in May. Nearly 80% of the May increase in final demand prices was attributable to a 2.8% increase in the index for final demand goods. Prices for final demand services rose by 0.3%.
Practical Implications for the Building Industry
For architects and spec writers:
- The cost gap between glass and metal is widening. If your project budget is squeezed, consider whether a slightly larger vision area and a leaner frame profile gets you better performance per dollar than upspeccing the IGU.
- Owner cost models built on Q4 2025 assumptions are stale. Year-over-year, flat glass is up over 6% and structural metal is up over 8%.
For glaziers and contract bidders:
- Hold the line on escalation clauses for aluminum and steel. Four consecutive months of ~1% increases in fabricated structural metal and ornamental metalwork is a trend, not noise.
- Glass quotes locked in May or June may not survive Q3 if energy stays elevated. Push for shorter validity windows on framing buyouts and longer windows on glass.
For window and curtain wall manufacturers:
- The divergence creates a margin-compression squeeze: you can't pass through metal increases as easily when your glass content is flat or declining. Product mix matters more than ever—unitized systems with higher metal content are seeing the cost pressure most acutely.
- Energy hedges and longer-term gas contracts are looking smarter every month.
For GCs running envelope buyouts:
- Watch for subs who are quoting flat numbers on long-lead curtain wall packages. Either they have firm supplier commitments in writing or they're going to come back for a change order.
The headline that 'glass prices dropped' is technically true, but it's the wrong story. The real story is that the cost structure of a commercial opening is splitting—and the metal half is moving the wrong way.