weft the content of the fibers in the fabrics is therefore roughly 50 round fiber and 50 square fiber the air permeability data are shown in table 1 for the 65 49 49 construction the fabric with the square fiber as the weft yarn has a permeability of 0 335 cc cm 2 u00b7 sec which is 57 lower than the 0 782 cc cm 2 u00b7 sec of the control sample with all round fibers for the denser 65 55 55 construction the fabric with the square fiber as the weft yarn has a permeability of 0 117 cc cm 2 u00b7 sec which is 45 lower than the 0 213 cc cm 2 u00b7 sec of the controlled sample with 100 round fibers in the second part of the experiments both the warp and the weft yarns employ the square fiber the air permeability is further decreased to 0 168 and 0 057 cc cm 2 u00b7 sec for the 65 49 49 and 65 55 55 constructions respectively the data are shown in table 1 in the production of the above fabrics the weaving tension is controlled to be 95 and 100 kg for the 65 49 49 and 65 55 55 constructions respectively the woven fabrics are subsequently heat set at.