This paper aims to find the relation between the air permeability of the unidirectionally oriented fiber assemblies at high porosity and these porosity, applying the Darcy's law to the onedimensional air flow through the fiber assemblies. According to the theory of hydrodynamics, the permeability for the bed of particles is proportional to ε³/ (1-ε) ², where ε represents the porosity of bed, and inversely proportional to the Kozeny constant. However, it was clarified by E. Lord that the Kozeny constant of fiber assemblies depends on the porosity. So, we have to determine the relation between the permeability and the porosity experimentally.
Experiments were performed with the use of unidirectionally oriented fiber assemblies made of cotton fibers and polyester fibers in the porosity region of 96.0-99.9% and on two fiber-axis directions relative to air flow; parallel and perpendicular. From the experimental results, it was found that :
K=R·ε³/ (1-ε) ^β
where K represents the air permeability, R and β being experimental constants depending on the two kinds of fibers used on this experiment (specimen 1 : 2.2 d, 30mm, 1.54g/cm³, 80t/cm cotton fiber. specimen 2 : 1.25 d, 38mm, 1.36g/cm³, mean no. of crimp 4.5t/cm polyester fiber) and the relation between the fiber-axis direction to air flow.
These results do not qualitatively correspond to the Kozeny-Carman's law, but show good agreement with the Lord's results obtained for cotton fiber assemblies in the porosity region of 96.0-99.0 (%).

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An experiment has been made to investigate the structural change, in the radius direction perpendicular to the fiber axis, of nylon gut yarns occured after twisting and heat setting by means of the micro beam X-ray techniques. The observations have revealed that : (1) a slight distortion of the-crystal lattice is found even near at the fiber axis, (2) considerable incline of the crystal axis b is found to the fiber axis, and (3) the steeper incline as well as rather distortion of crystal lattice are found at the outer layer of the yarn.

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In the textile industry, it should be a very important problem to develop textured spun yarns.
Three types of manufacturing processes for textured spun yarns were comparatively studied in this report.They are all false twist texturing processes but different in twist mechanism, i.e., the first one is a false twister of Suga type spindle, the second one is a frictional false twisting system, and the third one is a high-speed false twister provided with three pins spinners developed by authors.
Desirable results were obtained by using the third system. The third system can produce high-quality textured spun yarns economically and effectively.

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An attempt has been made to evaluate quantitatively the twisting shrinkage and the degree of .twisting (i.e., twist contraction force and untwisting moment) of hard plied yarns. Following fundamental equations have been obtained by experiments.
1) The twist shrinkage of the plied yarn, Rm, is given by :
R_m= (√1+ (2πNR) ²-1) - (k (√D·n/10⁵) ²-k (√D· (n-N) /10⁵) ²)
2) The degree of twisting of the plied yarn, M.T.C., is given by :
M.T.C.=√2D (N²+ (n-N) ²) ^1/2-√D·n
where, D : finess of a first twist yarn,
n : twist of a first twist yarn in turns per unit length,
N : twist of a final twist yarn in turns per unit length
R : radius of the cylinder on which the center line of a single yarn may exist, and
k : experimental constant determined by the twist method and twisting tension.
3) The relation between M.T.C. of the dry and wet twisting yarn is given by : M.T.C. of wet twisting yarn=β·(M.T.C. of dry twisting yarn)
where, β is an experimental constant determined by k of the dry and wet twisting yarn.

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