One of the fundamental stages in planning and developing any interlaboratory comparison is the selection and preparation of the test items to be distributed to the participants. In the case of compositional testing of textile materials, it is essential (1) to correctly identify the nature of the fibres which composes the fabric and (2) to check the homogeneity of the each test item. The Galician Laboratory of Consumer Products organized a proficiency testing (PT) in 2016 for textile fibres. Initial preparatory work was carried out with the assistance of the University of A Coruña, to identify the nature of the textile fibres using several complementary techniques specified in ISO/TR 11827 (e.g. optical microscopy, scanning electron microscopy, solubility tests and infrared spectroscopy). The fibres were compared with those from reference fabrics which were supplied by the Institute of Textile Research and Industrial Cooperation of Terrassa (INTEXTER). After the complete identification of the fibres, an assessment of homogeneity of the fabrics was performed according to the requirements in ISO 13528. Subsequently, five PT items were distributed and analysed according to the requirements set by ISO 1833 parts 3, 4, 7, 11 and 12, respectively. Eighteen laboratories from nine countries reported results, and the statistical treatment of results was performed according to ISO 13528. The assigned values were established by consensus, while the uncertainties were evaluated using the Naji Plot.