I remember reading that the soles of the feet absorb the most of what they touch! I always think of this when choosing shoes.
I've been searching for Safe Shoes ever since!!! I've learned about all of the REALLY harmful chemicals in leather and learned the traditional (and safe!) method of tanning leather is by using the animal's brain ("brain-tanned" leather)! Obviously, these shoes are EXTREMELY difficult to find!
The footbeds I wear include natural & toxin-free rubber (flip-flops), cork, toxin-free wood, vegetable-tanned (chrome-free) leather, toxin-free jute, organic cotton and earth (barefoot)!!!
I just relearned this when revisiting magnesium deficiency! With the mineral depletion of soil and current methods of sanitizing water, magnesium deficiency is widespread! I was still experiencing lower leg cramping/spasms during the night (although drastically reduced after starting to use magnesium oil spray and remineralizing water!); I found this article that suggested spraying magnesium oil on the footbed. Wallah! Miracle! I am using less oil but have not experienced a cramp since spraying directly on the footbed!!!!!! MIRACLE!