How Foldable Glass Changed Smartphones — Samsung UTG, Corning, and SCHOTT Compared

Every foldable phone sold today faces the same engineering tension: make the display glass thin enough to bend without snapping, yet strong enough to survive drops and daily pocket friction. Three companies — Samsung Display, Corning Incorporated, and SCHOTT AG — have taken fundamentally different paths to solving that problem. Below, we break down their ultra-thin glass technologies side by side, using published specifications and real device data rather than marketing claims.

What Is Foldable Glass and How Does Bendable Glass Work?

Foldable glass is ultra-thin glass — typically between 25 and 100 micrometers thick — that bends repeatedly without cracking. At that thickness range, a sheet of ultra-thin bendable glass behaves more like a flexible polymer film than the rigid panels in conventional smartphones. A 2026 study published in the Journal of the American Ceramic Society concluded that ultra-thin flexible glass with reduced Young’s modulus can achieve the mechanical compliance needed for foldable display applications while retaining the optical and surface properties that separate glass from plastic.

Behind bendable glass technology sits one principle: surface stress. When a sheet of glass bends, the outer surface stretches under tension while the inner surface compresses. Cracks start on the tension side.

The thinner the glass, the less strain the outer surface experiences at any given bend radius — which is why a 30 µm piece of glass can fold flat while a 500 µm piece shatters.

But thickness alone does not explain foldable glass durability. Manufacturers reinforce ultra-thin glass through chemical strengthening, an ion-exchange process that can transform the material’s surface properties — the glass is immersed in a molten potassium nitrate (KNO₃) bath at approximately 410°C. During this process, smaller sodium ions (Na⁺) in the glass surface are replaced by larger potassium ions (K⁺), creating a compressive stress layer.

Research published by the Korean Ceramic Society shows this process generates peak compressive stresses between 300 and 2,000 MPa — enough to withstand crack propagation during repeated folding cycles.

Samsung UTG vs Corning vs SCHOTT — Specs at a Glance

Three distinct approaches dominate the foldable glass market. Samsung Display was the first to commercialize UTG glass for consumer foldable devices. SCHOTT holds the Guinness World Record for producing the thinnest glass on Earth. And Corning Incorporated — the company behind Gorilla Glass — is developing a variable thickness glass with its own ion-exchange strengthening process. Here is how their published specifications compare.

Bend Radius, Thickness, and Fold Endurance

Three numbers define ultra thin glass performance in foldable devices: bend radius, thickness, and fold endurance. These parameters are interdependent — changing one forces trade-offs in the others.

Samsung’s decision to increase UTG thickness from 30 µm to 50 µm between the Galaxy Z Flip 5 and Z Flip 6 illustrates this trade-off. Thicker glass means a slightly larger bend radius and more visible crease — but it also means better drop resistance and reduced screen deformation over time. Android Headlines reported that the thicker UTG panel in the Z Flip 6 makes the screen harder and more scratch-resistant while reducing the display crease at the center.

SCHOTT claims the tightest achievable bend radius in the industry: less than 1 mm after chemical strengthening. That figure comes from their Xensation Flex product line, where the glass thickness can be tuned from 25 to 210 µm depending on the device manufacturer’s requirements. Their published fold endurance of 300,000+ cycles exceeds Samsung’s 200,000+ figure — though the two companies may use different testing protocols, making direct comparison difficult.

Looking ahead, TrendForce reports that Samsung is developing a dual-UTG structure for the Galaxy Z Fold 8. By layering two sheets of ultra-thin glass with different properties, Samsung aims to reduce crease visibility by another 20% compared to the Z Fold 7 while maintaining fold endurance above 200,000 cycles.

Scratch Resistance and Surface Hardness

Scratch resistance is the single most common complaint from foldable phone owners — and the cause is often misunderstood. Scratches users see on their foldable screen typically come from the soft protective film layered on top of the cover glass, not from the glass itself.

Chemically strengthened ultra-thin glass reaches a Mohs hardness of 6 to 7, comparable to standard smartphone glass. However, foldable phone manufacturers apply a thin polymer protective layer — usually thermoplastic polyurethane (TPU) or colorless polyimide (CPI) — over the UTG to absorb impact and prevent glass fracture.

That protective film has a pencil hardness of roughly 2H, corresponding to a Mohs rating of just 2 to 3. As The Verge explained in their Z Flip teardown, the glass underneath is genuinely scratch resistant — but the film on top scratches as easily as any plastic surface.

SCHOTT’s chemical strengthening increases edge strength by 4 to 10 times depending on glass composition and processing parameters. Samsung uses a proprietary intensifying process that injects a hardening material into the UTG to achieve consistent hardness throughout the sheet. Both approaches target the same goal: make the glass durable enough that the protective polymer layer becomes the weakest link — and eventually, unnecessary.

How Foldable Glass Is Manufactured

Producing glass thinner than a human hair requires a manufacturing process so precise that only a handful of facilities worldwide can achieve it. Two primary production methods — down-draw and fusion draw — each have distinct advantages for foldable screen technology.

Down-Draw Process (SCHOTT)

SCHOTT uses a down-draw process where molten glass flows vertically downward through a forming zone, creating a continuous ribbon. Precise temperature control and draw speed determine the final thickness. SCHOTT’s method produces glass ribbons from 25 to 210 µm and can be adapted for rollable reel-to-reel processing — where the glass is wound onto spools like film, enabling high-volume manufacturing.

Fusion Draw Process (Corning)

Corning’s fusion draw process feeds molten glass over a V-shaped trough, where two streams flow down opposite sides and fuse at the bottom. Because the surfaces never contact equipment, the resulting glass needs no polishing — a critical advantage for optical clarity. According to industry reporting, each fusion draw machine costs upward of $200 million, which helps explain why this innovation has been slower to reach consumer electronics at scale.

Chemical Strengthening: The Final Step

Regardless of the forming method, all foldable glass undergoes chemical strengthening. A standard process involves immersing the glass in a molten potassium nitrate (KNO₃) bath at approximately 410°C for 4 to 16 hours. During this ion-exchange process, smaller sodium ions in the glass surface swap with larger potassium ions from the salt bath, creating a compressive stress layer on the glass surface — with published values between 300 and 2,000 MPa depending on glass composition and processing time.

Research from the Korean Ceramic Society notes that spray-based KNO₃ application is emerging as an alternative for ultra-thin sheets, since the traditional dipping method can damage glass below 50 µm due to solution resistance.

Which Phones Use Each Type of Foldable Glass?

Samsung’s monopoly no longer exists among foldables in the phone market — the UTG supply chain reflects that shift. Multiple glass suppliers now compete for OEM contracts, with each device manufacturer exploring different device designs, glass sources, and thickness targets.

One surprise in this supply chain: Samsung does not always use its own glass. Korean industry publication THE ELEC reported that SCHOTT supplied all the UTG for the Galaxy Z Fold 3 in 2021. Meanwhile, Nippon Electric Glass entered the market in 2025 with Dinorex UTG — adding a fourth major supplier and giving OEMs like Xiaomi more sourcing options for their foldable device designs.

Apple’s anticipated foldable iPhone, widely reported for a September 2026 launch, is expected to use Samsung Display’s screen technology with ultra-thin glass. According to MacRumors, Apple is testing ultra-thin flexible glass panels with uneven thickness — thinner in the fold zone for flexibility, thicker elsewhere for rigidity — aiming to make the display crease invisible.

Foldable Glass vs Plastic Displays — Why Glass Wins

Before UTG became commercially viable, every foldable phone used colorless polyimide (CPI) as its display cover. Earlier models — the original Galaxy Fold (2019) and Motorola Razr (2019) — both relied on plastic. Switching to real glass solved several problems but introduced new constraints that continue to transform the foldable display industry.

Consider the transmittance gap — 91-92% for UTG versus 87-90% for CPI, per data from a PMC-published study on flexible display cover materials — which may sound small on paper, but becomes noticeable under direct sunlight. Higher transmittance means brighter, more vivid colors and better outdoor readability, important for a mobile device that users interact with hundreds of times daily.

Since 2021, every major foldable phone has launched with UTG rather than bare CPI as the structural cover layer. CPI still appears as a thin protective coating on top of the glass, but the era of plastic-only folding screens is effectively over.

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