It is essential to know the structure of textile fibers so as to get information about their physical structure. Hence the various methods to investigate the structure of textile fibers are addressed. The various methods used to investigate the physical properties of fibers are X-ray, FTIR, DSC, birefringence, etc. The most known physical properties of textile fibers can be categorized as the density of fibers, moisture, thermal, mechanical, electrical, and optical properties. Morphology of fibers: under this topic crystalline and amorphous composition will be studied. Investigation of fiber structure: The X-ray method is mainly used for calculating the crystal and amorphous fraction of the fiber. It is also used for the fiber orientation study. FTIR is mainly for the investigation of the functional group present in the fiber. DSC is used for the thermal property study of fibers like glass transition, melting, and crystalline temperature. It also used for the calculation of the percent Crystallinity of fibers. The physical properties of fibers are also studied.