# How do foldable phones work? The bendable screen, the hinge and the crease, explained

> Glass thinner than a hair, OLED pixels on plastic and a hinge that curls the screen into a teardrop: what lets a phone fold 200,000 times, and why the crease never fully goes away.

- Publisher: NextDiff (https://nextdiff.com/)
- Section: Hardware
- Author: NextDiff Editorial
- Published: 2026-10-29T05:07:22.849Z
- Updated: 2026-10-29T05:07:22.849Z
- Canonical URL: https://nextdiff.com/posts/how-do-foldable-phones-work/
- Topics: foldables, smartphones, iphone, apple

## In short

Foldable phones use an OLED screen built on flexible polyimide plastic instead of glass, covered by ultra-thin glass about 30 micrometres thick and a protective film. A hinge controls how tightly the screen curves. Samsung rates its foldables for 200,000 folds; the faint crease comes from repeated squeezing and stretching at the fold line.

## Key takeaways

- A foldable screen is an OLED panel on flexible polyimide plastic, under ultra-thin glass (about 30 micrometres) and a protective film.
- The hinge sets the bend shape: newer "waterdrop" hinges curl the screen into a wider teardrop loop, which spreads stress and lets the phone close flat.
- The crease comes from the fold line being squeezed and stretched every time; makers reduce it but none has removed it.
- Foldables are still about 2.5% of smartphone shipments (Counterpoint, Q3 2025), led by Samsung and Huawei, with Apple joining in 2026.

**How do foldable phones work?** A foldable phone uses an OLED screen built on flexible plastic instead of rigid glass, covered by glass so thin it bends (about 30 micrometres, thinner than a hair) and a protective film. A hinge underneath controls how tightly the screen curves, so it can bend hundreds of thousands of times without cracking.

![Samsung Galaxy Z Flip standing half-open at 90 degrees, its screen bending at the hinge](/media/fe846bd8cca44de297f7.jpg)
*Image: Grace R. Samson (CC BY 4.0, via Wikimedia Commons)*

That's the short answer. The long one explains why every foldable still has a faint crease, why the first Samsung Galaxy Fold broke in reviewers' hands in 2019, and why Apple took until 2026 to ship one.

## How do foldable phones work? The bendable screen

Think of a paperback book. Bend one page and it's fine. Glue ten pages together and try to fold them flat, and the inside pages wrinkle while the outside ones tear. A foldable screen is that stack of pages, so the trick is making every layer as thin and stretchy as possible.

A normal phone screen is an OLED panel built on a sheet of glass, under a thick cover glass. Neither can bend. A foldable swaps both:

- **The base:** the OLED pixels are built on a plastic film called polyimide, which survives being curled.
- **The pixels:** OLED pixels make their own light, so there's no rigid backlight layer to crack. That's why every foldable uses OLED, not LCD.
- **The cover:** instead of thick glass, there is **ultra-thin glass (UTG)**. Samsung Display [introduced its UTG in February 2020](https://news.samsung.com/us/samsung-utg-glass-foldable-display-easily-bendable-ultra-thin-glass) on the first Galaxy Z Flip. Reports put it at about 30 micrometres, chemically strengthened so it bends instead of snapping.
- **The film on top:** a plastic protective layer, the part your finger actually touches. It looks like a screen protector, but it is part of the display.

![NextDiff diagram: the layers inside a folding phone screen and why a waterdrop hinge reduces the crease](/media/8e7d4e46ab1b4755a8a8.jpg)
*Diagram: NextDiff*

## What does the hinge do?

The hinge is the other half of the answer. It holds both halves of the phone, sets the angles the phone can stop at, and, most importantly, decides the shape the screen takes when closed.

Early hinges bent the screen into a tight U. That puts all the stress on one line, and it left a visible gap between the two halves. The newer **"waterdrop"** design lets the screen sink into the hinge and curl into a teardrop-shaped loop. The curve is wider, so the stress spreads out, and the two halves can close flat. Samsung moved its Galaxy Z Fold5 to this kind of hinge in 2023, and [Android Central's hands-on](https://www.androidcentral.com/phones/samsung-galaxy-z-fold-5-hands-on) found that it finally folded completely flat.

Hinges are now small machines. Apple says the iPhone Duo's hinge has more than 100 components, plus a titanium plate under the screen and glass layers that can slide against each other to relieve bend stress, as we reported in our [iPhone Duo launch story](/posts/iphone-duo-release-date-price-sold-out/).

## Why do foldable phones have a crease?

Every fold squeezes the inside of the bend and stretches the outside. Do that 100 times a day and the layers deform very slightly along the fold line. Light then reflects off that line differently, and you see a crease, especially at an angle or on a white screen.

![Samsung Galaxy Z Fold 5 opened flat, with a faint vertical crease visible down the middle of the inner screen](/media/1cea9b40554c4cab9f8d.jpg)
*Image: Vosveteit.sk (CC BY 3.0, via Wikimedia Commons; cropped)*

Makers can make the crease shallower, with wider hinge loops, support plates and matte coatings, but none claims to have removed it completely. Apple's wording for the iPhone Duo is that the design "minimizes crease visibility", and reviewers said it is barely noticeable head-on ([our review roundup](/posts/iphone-duo-review-roundup/)).

## How many times can a foldable phone fold?

Makers test this with folding machines. Samsung said the Galaxy Z Flip's glass was certified by the testing firm Bureau Veritas for **200,000 folds**, and it has used that figure for its foldables since. That's about 100 folds a day for more than five years. For the Galaxy Z Fold7 display, Bureau Veritas verified **500,000 folds**, according to [Cybernews' report on the test](https://cybernews.com/gadgets/samsung-galaxy-z-fold-test/). Lab tests run at room temperature with no dust, so real-world life depends on how you treat the phone.

## Examples: the main types of foldable phone

![Samsung Galaxy Z Fold 8 Ultra, Galaxy Z Fold 8 and Galaxy Z Flip 8 on display stands](/media/599cb9dadcfd48058abf.jpg)
*Image: Dinkun Chen (CC BY-SA 4.0, via Wikimedia Commons)*

- **Book-style ("Fold"):** a normal phone outside that opens into a small tablet. Examples: Samsung Galaxy Z Fold series, Google Pixel Fold line, Huawei Mate X line and Apple's iPhone Duo (5.4-inch outside, 7.6-inch inside, from $1,999).
- **Flip-style (clamshell):** a full-size phone that folds in half to pocket size, like old flip phones. Examples: Samsung Galaxy Z Flip7 (6.9-inch inside, 4.1-inch cover screen) and the Motorola Razr line.
- **Tri-fold:** two hinges and three panels that open to tablet size. Examples: Huawei's Mate XT and Samsung's Galaxy Z TriFold.

They're still a niche. Counterpoint Research says foldables hit their [best quarter ever in Q3 2025](https://counterpointresearch.com/cn/insights/global-foldable-smartphone-market-q3-2025), up 14% from a year earlier, yet they were only about **2.5% of all smartphones shipped**. Samsung had about 64% of foldable shipments that quarter and Huawei about 15%, [according to the same data](https://www.malaysianwireless.com/2025/12/counterpoint-samsung-foldables-q3-best-sellers/).

## Foldable vs flip vs normal phone: how do they compare?

| | Book-style foldable | Flip foldable | Normal phone |
|---|---|---|---|
| Open screen | ~7.6–8 in, tablet-like | ~6.7–6.9 in | ~6.1–6.9 in |
| Closed size | phone-sized, thicker | about half a phone | one size |
| Crease | yes, faint | yes, faint | no |
| Cover glass | ultra-thin glass + film | ultra-thin glass + film | thick toughened glass |
| Main benefit | two apps side by side, reading, video | pocketable, outer screen for quick use | cheapest, toughest, thinnest |
| Typical price | highest (around $1,800–2,000) | mid-to-high | any |

## Why it matters

Foldables are the biggest change to phone shape since the iPhone era began. A book-style foldable puts a tablet in your pocket, which matters for reading, spreadsheets, video and running two apps at once. Flip phones trade size for pocketability. With Apple, Samsung, Google and Huawei all selling one, app makers now have reason to design for screens that change shape, which is why Android and iOS both added split-screen layouts for them.

## Common misconceptions

- **"The screen is plastic, so it scratches like plastic."** Older foldables did have plastic-only covers. Since 2020 most use ultra-thin glass under the film, which resists scratches better, though still less than a normal phone's glass.
- **"Peel off the screen protector."** Don't. In April 2019, several Galaxy Fold review units broke after reviewers removed what looked like a screen protector but was part of the display, and Samsung [delayed the launch](https://www.theregister.com/2019/04/22/samsung_delays_fold_smartphone/). Some units failed even with the layer left on.
- **"The crease means it's breaking."** A faint crease is normal from day one. Cracks, bubbles or dead lines along the fold are the warning signs.
- **"Foldables are waterproof like normal phones."** Many now have IPX8 water resistance, but dust is harder to keep out of a hinge, and few foldables carry a full dust rating.

## Latest news

- [iPhone Duo release date: Apple's $1,999 foldable goes on sale 23 October](/posts/iphone-duo-release-date-price-sold-out/)
- [iPhone Duo review roundup: the best foldable yet, say reviewers, but most say wait](/posts/iphone-duo-review-roundup/)
- [Oppo Find X10 Pro Max: three 200MP cameras for €1,799](/posts/oppo-find-x10-pro-max-price-specs-india-launch/) (a flagship slab phone, for comparison)

## Questions readers ask

### How do foldable phones work?

They use a flexible OLED screen built on plastic instead of glass, covered by ultra-thin bendable glass and a protective film. A hinge underneath controls the curve so the screen bends without cracking.

### How do foldable phone screens not break?

Every layer is made extremely thin, so it bends instead of snapping, and the hinge keeps the bend wide rather than sharp. Samsung says its foldables are certified for 200,000 folds, about 100 a day for five years.

### Why do foldable phones have a crease?

Each fold compresses the inside of the bend and stretches the outside, which slightly deforms the layers along the fold line. Light reflects off that line differently, so you see a faint crease. Better hinges make it shallower but do not remove it.

### How do flip phones work?

Modern flip phones such as the Galaxy Z Flip and Motorola Razr fold a full-size flexible screen in half from top to bottom. A small cover screen on the outside shows notifications when closed.

### Are foldable phones worth it?

They are worth it if you want a tablet-sized screen or a pocket-sized phone and accept a higher price, a faint crease and less durability than a normal phone. If price and toughness matter most, a regular phone is the safer buy.

## Sources

- [Samsung Newsroom — Samsung Display introduces foldable display with ultra-thin glass (Feb 2020)](https://news.samsung.com/us/samsung-utg-glass-foldable-display-easily-bendable-ultra-thin-glass)
- [Android Central — The Galaxy Z Flip's foldable glass (UTG, Bureau Veritas 200,000 folds)](https://androidcentral.com/galaxy-z-flips-foldable-glass-heading-non-samsung-devices)
- [Android Central — Samsung Galaxy Z Fold 5 hands-on (waterdrop hinge folds flat)](https://www.androidcentral.com/phones/samsung-galaxy-z-fold-5-hands-on)
- [Cybernews — Samsung says Galaxy Z Fold 7 display survives 500,000 folds](https://cybernews.com/gadgets/samsung-galaxy-z-fold-test/)
- [Counterpoint Research — Global foldable smartphone market Q3 2025](https://counterpointresearch.com/cn/insights/global-foldable-smartphone-market-q3-2025)
- [Malaysian Wireless — Counterpoint: Samsung 64%, Huawei 15% of foldables in Q3 2025](https://www.malaysianwireless.com/2025/12/counterpoint-samsung-foldables-q3-best-sellers/)
- [The Register — Samsung delays Galaxy Fold after review units break (Apr 2019)](https://www.theregister.com/2019/04/22/samsung_delays_fold_smartphone/)
- [Apple Newsroom — Apple unveils iPhone Duo](https://www.apple.com/newsroom/2026/09/apple-unveils-iphone-duo/)
- [Wikipedia — Foldable smartphone](https://en.wikipedia.org/wiki/Foldable_smartphone)