Which man-made fibre is known to be difficult to dye?

Polyester is known to be difficult to dye due to its chemical structure and the strong molecular bonds within the polymer. Unlike other fibers, polyester requires specific dyes and high temperatures to achieve effective dyeing. Its hydrophobic nature means it does not easily absorb water-based dyes, making the dyeing process more challenging.

Rayon and lyocell, while they have their unique properties, are more amenable to dyeing because they are regenerated cellulose fibers that can absorb dyes more readily. Acetate has its own dyeing challenges, particularly due to its sensitivity to heat and certain dye types, but polyester remains the most notoriously difficult man-made fiber to achieve effective color penetration and fastness under typical dyeing conditions.