My favourite are Sandália Goóc, specifically the Geocasp, which are comfy, as steady on rough terrain as most shoes, and largely recycled. I would appreciate tips on how to get these outside Brazil. Seems impossible?
Given that difficulty, I’m interested in the Xero sports sandals although they are rather expensive. They have an impressive warranty, though, and seem to weigh nothing.
A lower cost alternative might be lightweight folding sandals like flipsters.
Shoes are expensive new and subject to fluctuations in fashions; I prefer to buy them second-hand.
Skinners the sock-shoe are at least a low-material shoe. At EUR50/pair they are not cheap per gram but they look terribly convenient.