S.A. Hosseini Ravandi, M. Valizadeh, in Improving Comfort in Clothing, 2011. 2.3.2 Microfibers. Microfiber is defined as a staple fiber or filaments of linear density approximately 1 dtex or less, and above 0.3 dtex. Although acrylic, viscose and polypropylene are available for the production of microfibers, polyester and polyamide are the main source.