The seam strength of fabrics sewed by hand sewing methods was investigated in order to clarify the mechanical and morphological properties of Japanese traditional hand sewing. Two hand sewing methods were compared. One is “plain stitch, ” the other is “right angle stitch, ” which is defined as the stitch-formed seams on fabrics by a needle-like machine sewing. Silk and cotton fabrics and sewing threads were used.
1) The breaking strength of a 3 mm seam was higher than that of a 4 mm seam according to the stitch density, and the breaking strength of a seam with a right angle stitch was higher than that with a plain stitch because of the higher thread angle of the plain stitch.
2) The shrinkage of the plain stitch seam was higher than that of the right angle stitch seam in cotton and silk fabrics, which meant that the plain stitch is better than the right angle stitch for fabrics with weaker breaking strength.
3) The break holes of the fabrics sewed by the plain stitch were smaller than those sewed by the right angle stitch. These results explain why the plain stitch has been used for a long time to construct Japanese traditional costume, “Kimono.”