Braided sleeve is usually made of plastic (PET) and is used to manage cables to and from electronic circuits like an Arduino. Braided sleeve increases abrasion resistance, prevents cables from coming loose, looks nice and is cost effective. Of course, available in more than one color, and even in multicolor braids.
Tip for use: burn the ends of the braided sleeve together with a lighter (with the cables out of course), so the ends won’t unravel. A tie wrap (cable tie) also helps to maintain mechanical stability.