I think I remember seeing a screenshot showing that Xehanort's patterned coat trim is made from snakeskin, or at least it has a snakeskin like texture. I may be remembering this wrong though, plus I doubt it's easy to get one's hand on the stuff, unless if you go for fake snake leather.
I you look HD screenshots, you can see that the snake-like texture is only for Xehanort's boots. The texture of the coat is more like cotton or linen twill (you can see better on Eraqus' coat but it's the same for Xehanort)
I hope it will help you :-)












