Which fiber is NOT mentioned as part of microfibres?

The correct answer is cotton, as it is not typically categorized as a microfiber. Microfibers are generally defined as very fine fibers—less than 1 denier—that can be made from synthetic materials. Both polyester and nylon are commonly used to create microfiber fabrics due to their ability to be produced in extremely fine filament forms and their desirable characteristics such as strength, durability, and moisture-wicking properties.

Rayon, while not a synthetic fiber like polyester and nylon, can also be produced in microfiber form. It is derived from natural sources, primarily wood pulp, and can be processed into fine strands suitable for various textile applications.

In contrast, cotton fibers, although they can be spun very finely, do not fall into the microfiber category. Cotton is a natural fiber that doesn't typically exhibit the same properties as microfibers, such as enhanced water repellency and quick drying capabilities, which are key characteristics sought after in microfiber materials.