SEA-ISLANDS TYPE COMPOSITE FIBER HAVING EXCELLENT MOISTURE ABSORBABILITY, FALSE TWIST YARN, AND FIBER STRUCTURE

A sea-islands type composite fiber characterized in that an island component is a polymer having moisture absorbability, the ratio (T/R) of the thickness (T) of an outermost layer to the diameter (R) of the fiber on a transverse cross-section of the fiber is 0.05 to 0.25, and the moisture absorption rate difference (”MR) after a hot water treatment is 2.0 to 10.0%. The term "thickness of an outermost layer" refers to the difference between the radius of the fiber and the radius of a circumscribed circle formed by connecting apexes of island components located on an outermost periphery, and represents the thickness of a sea component in the outermost layer. Provided is a sea-islands type composite fiber which does not undergo the cracking of a sea component upon the volume expansion of a moisture-absorbable polymer that serves as an island component during a hot water treatment such as a dyeing treatment, rarely undergoes the formation of dying specks or fluffs when the composite fiber is formed into a fiber structure such as a woven fabric or a knitted fabric, has excellent quality, is reduced in the elution of the moisture-absorbable polymer, also has excellent moisture absorbability even after a hot water treatment such as a dyeing treatment, and also has dry touch inherent to a polyester fiber when the sea component is polyester.