It's a long shot, but I've found that "peau de lapin" seems to be shorthand for gesso (rabbitskin glue, also called rabbitskin), which is traditional for mounting canvases. It may be what makes those big mailbags practically indestructible and gives them that texture that is different from normal canvas.

For fun, too, though I doubt that it's relevant, you can Google "rabbitskin pouch" and get lots of references on pagan sites.