E-ink could be used by Apple for a folding cover screen.
According to a teaser tweet from analyst Ming-Chi Kuo, the illusive iPhone Flip may use technology akin to the Amazon Kindle
Apple has been testing a colour electronic paper display (EPD) for the cover screen of foldable iPhones as well as future iPad tablets, according to Kuo
The high refresh rate and high-resolution screens used in modern foldables are not the same as an e-ink screen. The benefit would be significantly longer battery life