Book or Flip? How Foldable Phones Work

Foldable phones have been on sale since 2019, when Samsung's first Galaxy Fold launch was delayed after reviewers' screens failed within days. The technology has improved a great deal since then, but foldables still make up only a small share of smartphones sold. Understanding how they're built explains both their appeal and their trade-offs.

Two main designs

Book-style foldables open like a book into a small tablet, usually around 7 to 8 inches across, with a regular-sized screen on the outside. Examples include Samsung's Galaxy Z Fold series and Google's Pixel Fold. They suit people who read, multitask or watch video on their phone and want a larger screen without carrying a tablet.

Flip-style foldables fold in half horizontally, like the flip phones of the 2000s, so a full-size phone becomes small enough for a pocket. Samsung's Galaxy Z Flip and Motorola's Razr are the best-known examples. They appeal mainly for compactness and style rather than extra screen space.

How a screen can fold

Regular phone screens use rigid glass. Foldables use a flexible OLED panel covered with either a plastic film or ultra-thin glass, a layer of glass thin enough to bend that Samsung introduced on its foldables in 2020. Ultra-thin glass feels more like a normal phone screen but is still softer and more easily marked than the hardened glass on regular phones.

The hinge is the other key part. It has to let the screen bend in a gentle curve rather than a sharp crease, support the phone at different angles, and keep out dust. Early hinges left visible gaps; newer "waterdrop" designs let the screen curl into a teardrop shape inside the hinge, which reduces the crease.

The crease

Almost all foldables have a visible or touchable crease where the screen bends. It's more noticeable at an angle and on light backgrounds. Most owners say they stop noticing it, but it's worth seeing in person before buying.

Durability

• Manufacturers test hinges for hundreds of thousands of folds, which equals many years of normal use.
• The inner screen's top layer is softer than regular phone glass, so fingernails and pressure can mark it.
• Dust and sand are a bigger risk than water for many models, since the hinge has moving parts.
• Screen repairs cost considerably more than on standard phones, so many owners buy extended protection plans.

Price

Book-style foldables are among the most expensive phones available, often well above the price of a flagship standard phone. Flip-style models are cheaper and sometimes priced close to regular high-end phones. Prices typically drop significantly when the next generation arrives, so buying the previous model is a common way to save.

Battery and weight

Two screens and a hinge add weight. Book-style foldables are usually noticeably heavier than standard phones, and flips, despite being compact, often have smaller batteries split across two cells on either side of the hinge. Battery life has improved with each generation, but it's worth checking independent battery tests if you're a heavy user.

Looking after a foldable

• Don't remove the factory-installed screen protector on the inner display; it's part of the screen's design, and replacements are usually done by the manufacturer.
• Make sure nothing, such as a card or crumbs, is on the screen before closing it.
• Keep the phone away from sand and fine dust, for example in a zipped bag at the beach.
• Avoid pressing hard on the inner screen with fingernails or a stylus not designed for it.
• Use a case designed for your model so the hinge isn't strained.

Resale value

Foldables have historically lost value faster than mainstream flagship phones, partly because of concerns about wear on the hinge and inner screen. That makes used and previous-generation models good value for buyers, but it's worth checking the hinge action and the inner screen carefully when buying second-hand.

Who they suit

A book-style foldable makes sense for someone who would otherwise carry a phone and a tablet, or who works on documents and email on the go. A flip makes sense for someone who wants a smaller phone in the pocket. For people who mainly want the best camera, battery life or durability for the money, a conventional phone is still the safer choice.

Software matters too

A larger folding screen is only useful if apps make good use of it. Android has added features for running two or three apps side by side and for continuing an app seamlessly when the phone is unfolded, but some apps still display as a stretched phone layout. Checking whether the apps you use most support large screens is worth doing before buying a book-style model.