Consumers like large displays on the mobile devices they use for reading an e-mail message or an e-book, but they also like to tuck those devices into their pockets. But the bigger the screen on a cell phone or an e-reader, the sooner it outgrows pocket size.

Now a hallmark feature of these screens - their rigidity - is changing. New technologies are developing that make displays flexible, foldable or even as rollable as papyrus, so that large screens can be unfurled from small containers.

One new mobile device, the Readius, designed mainly for reading books, magazines, newspapers and mail, is the size of a standard cell phone. Flip it open, though, and a screen tucked within the housing opens to a 5-inch diagonal display. The screen looks just like a liquid-crystal display, but can bend so flexibly that it can wrap around a finger.

Because the Readius is pocket-sized, but has a generous, supple screen, people with five minutes to spare in a taxi, bus or subway can use the dead time to open it, read a page or two of a book and then return the device to a shirt pocket, said Karl McGoldrick, the chief executive of Polymer Vision, the company in Eindhoven, the Netherlands, that created the device.

The Readius may even help stop people from obsessing over their e-mail: with the device, spare moments for reading may be put to a possibly better use - say, a novel by Stendhal. But if their good intentions fail, the device has a wireless connection to download e-mail as well as books.

The black-and-white display holds about 22 lines of a book page, depending on the font, all shown in the crisp black type provided by technology from E Ink, also used in Amazon's Kindle and other e-readers. The screen changes from one page to the next in about half a second, at the touch of a thumb.

The Readius will be introduced in England, Italy and Germany this fall, and in the United States early in 2009, McGoldrick said. Its battery lasts for about 30 hours of reading - long enough to get through ''The Red and the Black,'' and possibly a chunk of ''War and Peace.'' Pages can be read under a variety of lighting conditions, even including full sunlight, he said. The price is not yet set, but Thomas van der Zijden, vice president for marketing and sales, said the Readius would be more expensive than the Kindle, which is selling for $359.