Microfiber is composed of very finely woven fibers, defined by their thickness, or denier, which is the measurement of a fiber’s thickness. A high denier points to a material of higher thickness, a low denier is one of lower thickness.
For a material to be considered microfiber, it must be less than 1 denier in diameter.
For comparison, consider that fine silk measures at 1.25 deniers; thus, microfibers are made in the lab instead of forming naturally in nature. They can be made from wood pulp, or polyester and nylon polymers. Microfiber sheets are very thin, but are strong and exceptionally smooth and comfortable.