The AI accelerator crunch has moved to a 90% monopoly in glass cloth

Nittobo's T-glass is a low-CTE (coefficient of thermal expansion) glass cloth used in the organic core of IC substrates, the interconnect layer between a chip and its printed circuit board. It keeps large, high-heat packages dimensionally stable, which matters more as AI processors grow bigger and run hotter. Tom's Hardware reported on 9 March that the material sits inside every advanced AI chip package.

Prices have risen between 20 and 30%. Lead times for downstream materials such as copper-clad laminates have stretched from a normal 8 to 10 weeks to beyond 20.

"With T-glass supply even more constrained now, suppliers are no longer providing lead times," said Bill Ho, an analyst at Yuanta, according to Tom's Hardware.

The bottleneck is not easy to design around. Bilal Hachemi, an analyst at Yole Group who tracks the IC substrate supply chain, told Tom's Hardware that T-glass "has specific dielectric and CTE values that work better for the AI chips, especially for the organic core." Cheaper E-glass goes into lower-end chips such as microcontrollers and older mobile processors. For massive 2.5D and 3D packaging, and therefore for advanced AI accelerators, T-glass is the preferred option.

Nittobo is tripling capacity at its Fukushima plant in Japan, but Tom's Hardware reports that new supply will not arrive on the market until mid-2027. New production lines cannot be spun up overnight. The material requires specialized electric melting furnaces running between 1,600 and 1,700 degrees Celsius, and the process involves melting silica-rich glass, spinning it into yarn and weaving it into an ultrathin cloth. Hachemi also pointed to the industry's thin margins, saying that "any increase in demand for build-up materials, ABF material, or T-glass can cause potential shortage, because it's against the basics of this industry."

Bigger packages, more cloth

Hyperscalers are ordering ever-larger chip packages that consume more T-glass per unit. According to Nvidia data cited by Tom's Hardware, interposer sizes grew from 814mm2 for the Hopper architecture to 1,700mm2 for Blackwell, a 109% increase, with the forthcoming Rubin and Feynman generations scaling further. Bank of America estimates Nittobo's electronic materials segment will nearly double sales from 40.9 billion yen ($266 million) in 2025 to 87.7 billion yen by March 2028, with operating margins approaching 48%.

"Demand for T-glass cloth seems likely to grow more than originally expected," Takashi Enomoto, a research analyst at Bank of America, said, per Tom's Hardware. "The focus has been on growth in demand for thick T-glass for use in GPU and CPU semi packages, but now ultra-thin T-glass demand is likely to rise on a shift from E-glass to ultra-thin T-glass in leading-edge devices."

The scramble for allocation has already produced an unusual sight. Hachemi told Tom's Hardware that Nvidia reaching out directly to an upstream material supplier is unprecedented in that part of the supply chain. "For the first time, we are seeing Nvidia, the end customer, reaching out to the upstream material suppliers to secure the capacity and make sure they will get it," he said. The risk is that once Nvidia locks down its share, rival chip buyers are left fighting over the remainder.

Nittobo is not relying on Fukushima alone. It is doubling raw yarn capacity at its Taiwan plant and importing yarn back to Japan for cloth manufacturing. It has also struck a collaboration deal with Nanya Plastics to outsource some weaving. Tom's Hardware reports that by 2027 roughly 20% of Nittobo's glass cloth is expected to be woven by Nanya. Partnering with one of its biggest competitors is a fair measure of how tight the market has become.

The wider accelerator pipeline is not standing still. Microsoft's Maia 200, presented at Hot Chips 2026, is built on TSMC 3nm with a 750 Watt TDP, 7TB/second of HBM bandwidth across 6 HBM stacks, and 10,000 TFLOPS of FP4 performance, according to ServeTheHome's write-up of the session. Those packages still need substrate material that only a handful of suppliers can make.

Nvidia is meanwhile pushing AI deeper into its own design flow. Tim Costa, vice president and general manager of computational engineering at Nvidia, told journalists that AI and accelerated computing are moving "from productivity tools into being foundational engineering infrastructure," The Next Platform reported on 27 July. Cadence claims its AI Super Agents can deliver 40-times faster Register-Transfer Level validation cycles, and Synopsys says its agentic workflow can deliver validated RTL 50 times faster than other platforms.

None of that shortens the queue for T-glass. The substrate crunch is a reminder that the AI buildout depends on materials few people have heard of, made by companies with almost no competition.