A facsimile pocket herbal bound in limp, unsupported vellum in the sixteenth-century manner — no boards at all, just the vellum wrapper itself providing the structure, tied closed with a vellum thong rather than a clasp.
Limp vellum was the everyday binding of its period, cheap and durable, and it has come back into demand from readers who want a book that can genuinely live in a coat pocket rather than sit on a shelf.