What you should know about flexible mobile displays.

Samsung, LG, and others have been showing off flexible displays and even a prototype phone for years, but it's only now that bendy screens are going commercial.

Samsung's Galaxy Round and LG's G Flex raise a lot of questions about what a flexible display is and isn't, what the word really means, and just what kinds of benefits a bendable display would bring to a smartphone or any other gadget.

What is a flexible display anyway?

Colloquially, "display" means the thing you see when you look at your phone and navigate around. But more technically, display refers to the electronic material that sits beneath the glass or plastic cover (the part you actually touch) and is responsible for lighting up your phone.

So when Samsung and LG (or anyone) talk about a flexible display, they're talking about the organic light-emitting diode, or OLED, layer -- located beneath the cover glass -- that's now made using flexible materials (like plastic) rather than rigid glass.

Companies like LG and Samsung have spent years demoing flexible displays that sit on their own outside of any device. These eye-catching products faithfully show off the interface you're supposed to see -- say a grid of icons -- without bending or breaking. Samsung's Galaxy Round represents the first time that a phone maker is bringing a flexible display to market, followed by the LG G Flex.

Why would anyone want a flexible display anyhow? What are the benefits?

As CNET has noted before, the benefits for a curved display like the Round and Flex aren't immediately clear, though one could be increased readability and less glare from a curved display.

There are some pretty significant benefits for displays that can flex. For one, they could be less prone to breakage when dropped, largely because they might use plastic, which has some give, instead of glass. Plastic also can make the devices thinner and lighter, and it can allow for products in different shapes beyond the standard rectangular screen.

Note that this may not always be the case. Even plastic can break if you stress it enough, and glass-makers are also designing flexible glass, but more on that below.

Still, the durability issues raises the question: Why not just make a regular phone with a plastic display? We'll likely see that too, some experts say, but there are some things a flexible display can do that others can't.

While some gadget-watchers are incredulous about the practicality of a scrollable phone, others see the benefit in trying to make them anyhow. NPD DisplaySearch analyst Paul Semenza is one of them. "I don't think anyone developing them knows the value of curvature or flexibility yet," he told CNET.Imagine being able to fold up your phone or tablet and put it in your pocket, or unroll a screen to serve as a map. These could even be incorporated into clothing or jewelry or other items where the screen needs to have some give. The future potential for flexible displays is huge if hurdles are overcome, even though we may not yet know exactly what their uses will be.

What are the hurdles to making a flexible smartphone?
It takes much more than a bendy screen to make a phone you can flex. Right now, batteries and other circuitry are unyieldingly straight. The durability of a bendable phone and its internal parts are also in question. Depending on the design, you may need to have a flexible display, cover material (like plastic or glass), arching batteries, and forgiving silicon.

Some of this is already in the works. LG announced new battery tech for three kinds of juice packs that can curve, squeeze into tight spaces, and even contort like a pretzel. Time will tell if these produce and hold enough charge to competitively power a smartphone.

In addition, devices can be designed so they have a sort of rigid spine that stores the components that can't be flexed, while the rest of the gadget moves freely. We know that these various flexible designs are possible based on concept devices shown by Samsung and others.

Along with making the guts flexible comes another big challenge -- manufacturing these devices and displays at high volumes. Phones that move will undoubtedly cost more than standard smartphones when they first hit the market, but after the industry nails down more efficient manufacturing, the cost to make the phones will surely drop, along with their sticker price.

Even though the Galaxy Round and G Flex's displays are curved, not bendable, they're undoubtedly still tough to manufacture efficiently at high volumes.

Which is better, flexible OLEDs or LCDs?
When companies show off displays being curved, bent, folded, or rolled, they're typically using OLED. While it's possible to curve an LCD, it's not as easy or as effective as curving OLED, according to the experts we spoke with.

Are the flexible phone screens made of glass?
We wish we could tell you for sure, but we just don't know yet. Samsung isn't sharing specific details, and Corning (makers of Gorilla Glass) declined to comment. There's some speculation that Samsung would be using a plastic polymer screen, but it appears more likely that the Round, for one, has a thin layer of glass that has been bent into a curved shape.

So everyone will just switch to plastic, right?

Switching to a plastic display would certainly allow a device to be truly flexible, but plastic comes with its own problems. It has different properties than glass, which means manufacturers have to find ways to use it without compromising the screen's crystal-clear image quality or responsiveness.

One big issue for plastic is that it's semipermeable, which could allow air and water to leak into the device. To avoid this, companies can coat the plastic and apply barrier layers, and some have experimented with glass/plastic hybrids. While there are still some hurdles to overcome, industry watchers say it's only a matter of time -- and money -- before this is no longer an issue.

What else is a flexible display good for?

Although we have yet to determine just how practical or even desirable a smartphone is that you can bend and twist, there are some good, practical uses for display technology that can be formed into S-curves and still respond to touch. Here's one: a wraparound touch display that covers the band of a smartwatch or other wearable. And here's another: an all-touch car dashboard that spills far beyond the confines of its usual 8-inch rectangular home.