Double-sided Slippers

Double-Sides Slippers, created by Zhang Xun and Li Cheng, are designed to enable the user to wear the slippers from both directions, avoiding the hassle of rearranging the slippers in the event that they're upside-down.

The material must be soft enough to accommodate the user's foot without springing, but resilient enough to return to its original form after removing it.  The only problem is that the right and left slippers are not interchangeable; if one goes into all the trouble of creating these, wouldn't it be a simple extension to make the slippers vertically symmetrical as well?

Source: Red dot