Ask HN: Why isn't there a foldable e-ink book reader?

What would be the point? Books have the shape they do because paper is two-sided, and they are optimized for information density. There's no inherent value to seeing one page next to another, and even less in having a fold.

I've been using a Kindle for many, many years - after reading paper books for many, many years - and I've never wanted this, personally. One of the great things about an ereader is its incredible portability. Even if adding a second half was a negligible size change, I wouldn't want to bother folding and unfolding the thing every time.

For same reason, why e-ink not become secondary screen on mobiles - I've seen few examples, and all just not sold good enough to be considered as persistent solution.

Possible, this is because LCD/OLED screens are cheap and good enough for most cases, so too tiny market left for e-ink.

Portability is probably a big thing, the fact that Kindles are advertised as being significantly thinner than a paper book. There is also just a large lack of innovation in that area, due to the fact that Kindles sell no matter what. Very few improvements are made but new Kindles always perform well.

Perhaps it could be a KickStarter project? As long as it allows you to read all current eBook formats. I wouldn't mind if it could also be used as a tablet.

There are hinged paper versions which still work well.