What is a characteristic of filament fibres?

A filament fibre is characterized by its long length, which distinguishes it from staple fibres that are shorter. Filament fibres can be either natural, such as silk, or synthetic, like polyester or nylon. The long structure of the fibre allows for a smooth and lustrous finish in textiles, making them desirable for various applications, such as in clothing, upholstery, and other fabric uses.

In the context of the other choices, while filament fibres can be synthetic, they are not exclusively unnatural—natural fibres like silk also fall into this category. The option stating that filament fibres are always short is inaccurate since it directly contradicts the definition of filament fibres. Regarding the spinning into yarn, filament fibres typically do not need to be spun since they can be used directly in their filament form, which is different from how short staple fibres are processed.