This document specifies a method, using acetone, to determine the mass percentage of acetate, after removal of non-fibrous matter, in textiles made of mixtures of acetate with wool, animal hair, silk, protein, cotton (scoured, kiered, or bleached), flax (or linen), hemp, jute, abaca, alfa, coir, broom, ramie, sisal, cupro, viscose, modal, polyamide, polyester, polypropylene, acrylic, elastolefin, elastomultiester, melamine, polypropylene/polyamide bicomponent, polyacrylate and glass fibres. It is not applicable to mixtures containing modacrylic fibres, nor to mixtures containing acetate fibres that have been deacetylated on the surface.