Air textured yarn(ATY) samples were prepared from hollow PET 75/24(SDY) and PET 100/192(SDY) under the different air pressures(6 bar~12 bar) and interlaced yarn(ITY) samples were prepared from hollow PET 75/24(POY) and PET HS 40/24 under the different air pressures(3 bar~6 bar) and two speeds(400 and 450 m/min) to determine their hollowness and physical properties. Measured physical properties included unit weight, tenacity, elongation, and dry and wet shrinkage. The important results of this study were: 1) The hollowness of ATY samples decreased with increasing air pressure. The hollowness decreased to 27% when the air pressure increased from 6 bar to 12 bar and the rate of decrease was most noticeable above 9 bar. In addition, the unit weight of samples increased with the air pressure and the rate of increase was most noticeable above 8 bar. However, there was little effect of air pressure on the physical properties. 2) The hollowness of ITY samples decreased with increasing the air pressure. The hollowness decreased to about 34% when the air pressure increased from 3 bar to 6 bar and the rate of increase was most noticeable above 4 bar. The number of entanglement of the samples increased with the air pressure. However, there was little effect of the air pressure on the physical properties.