These shoes --manufactured in Fujian, China (model KSS-8859, mesh water shoes with three false laces and a trimmed topline border), sold under various brand names in Amazon and other markets by reselling exporters-- are made of synthetic materials (PU, EVA, MD).  They are very light, inexpensive, and cheaply made.

The shoes I got were badly assembled, with protruding rough seams on the inner surface, which after a short time of testing caused a skin irritation of the top of the foot: [ 1 ] the hanging inner seam of the shoe's tongue where it joins the upper (Fig. A, rectangle), and [ 2 ] the edge of the label stitched midway the tongue's inner face, an edge which bends inwards towards the skin (Fig. B, rectangle).  In addition, the tongue often slides to one side. This exposes the chafing ends of the elastic false laces and the protruding bottom of some lace-hole grommets, which then replace the annoying edge of the label's stitch (now slid to one side) in irritating the top-most part of the foot.

I did not get to try them while kayaking, but the elastic laces and sole are not appropriate for sucking river mud or banks with loose pebbles. I ignore what proportion of these shoes have the same annoying features, but, given the non-trivial number of equivalent customer complaints, this is not the case of an occasional faulty pair. I was unwilling to spend time and discomfort in trying to break the shoes, so I returned them.