A strand of microfiber is much thinner than a human hair, and thus much finer than most textile fibers such as cotton.
According to Starfiber®, a leading manufacturer of microfiber products:
Each strand of microfiber is comprised of two components: wedge-shaped polyester filaments and a core of nylon. Made of both oil-attracting and water-attracting polymers, these strands are woven into masses of tiny "hooks & loops". The sharp edges of millions of these fibers cut through dried-in stains, attracting and absorbing dirt and micro-particles, eliminating the need for additional chemical cleansers.
Microfiber is not treated with any chemicals. The capillary effect between the filaments and nylon core creates a high absorbency, which in turn, enables the fiber to clean and polish at the same time. Therefore, only water is needed to clean most types of surfaces.
How microfiber works:
Microfiber picks up and traps dust, dirt, grease, and particles inside the "star-shaped" grooves of the fiber. Each cloth and mop pad is made up of over 2 million yards of microfiber for many times the cleaning power of an ordinary cleaning cloth or pad.
Reference:
Starfiber®Microfiber Cleaning Products