sample c has been reduced by 252 cm 3 cm 2 u00b7 sec 495 ft 3 min ft 2 in comparison to the control by the insertion of 1 8 mm hollow monofilaments similarly the air permeability of samples d and e have been reduced by 276 cm 3 cm 2 u00b7 sec 542 ft 3 min ft 2 and 312 cm 3 cm 2 u00b7 sec 613 ft 3 min ft 2 respectively by insertion of 1 9 mm and 2 0 mm diameter hollow monofilaments a net change in air permeability of 332 cm 3 cm 2 u00b7 sec 652 ft 3 min ft 2 in comparison to the control is realized when a larger 2 1 mm diameter hollow monofilament is inserted into the same position as in sample f table 3______________________________________effect on spiral fabric air permeability obtainedby inserting hollow monofilaments made from pet sample noparameter a b c d e f______________________________________spiral count 6 5 6 5 6 5 6 5 6 5 6 5 cm sup 1 hinge yarn 2 4 2 4 2 4 2 4 2 4 2 4count cm sup 1 hinge yarn 0 10 0 70 0 70 0 70 0 70 0 70diameter mm inserted weft n a 0 45 u00d7 1 8 1 9 2 0 2 1size mm 2 2inserted weft n a 100 63 4 74.