Trace elements in textile fibers were analyzed by the in-air particle induced X-ray emission (PIXE) method. Individual fibers were used as a target, representing minute material available in forensic or archeological applications. For quantification of the concentrations, the X-ray production was assumed to occur in a thin cylindrical target that intersects the central part of the beam. The irradiated volume and the distribution of escape lengths were calculated in the model. The impact beam intensity was axially symmetric Gaussian, as shown by calculation and cross-scan measurements. The normalization procedure relied on the argon signal from the air, which was checked by the chopper method. For a set of fibers, elements characteristic of the fibers and their dressings were determined.