Sony had a never before seen prototype of flexible electronic paper display technology at the 2010 Dealer Convention. Usually, E-paper has used glass substrate in the past but this new technology uses plastic substrate. Glass substrate is heavier and more prone to damage than plastic substrate, which is much lighter and can also be bent. Electronic paper with plastic substrate is also very difficult to break even when you drop it, and can even be rolled up like real paper.
Source: Sony Insider