Abstract: An electret fiber sheet has polarized charges on its surface and preferably has charges in ordered orientation across it. The polarized charges are present in an amount of at least 7.times.10.sup.-11 C/cm.sup.2. Such sheets are formed to have a dust collecting efficiency. Sheets having an amount of polarized charge even as high as this are nevertheless stable when they have a maximum orientation energy of depolarization of at least 0.2 eV.Such an electret sheet can be obtained by a process comprising placing a fiber sheet between a non-contact type voltage-application electrode and an earth electrode confronting each other and supplying electricity (voltage>3 kV; current density>1.times.10.sup.-6 mA/cm.sup.2) between the electrodes, provided that the fiber sheet has a weight less than 80 g/m.sup.2 and a covering factor at least 60%.

Abstract: A spun-type yarn having a unique configuration and useful properties is manufactured by a novel process which comprises forming a ribbon-shaped fiber bundle being substantially free from twists and composed of randomly oriented continuous filaments, each of which comprises random bends and loops along its length, and then false twisting the ribbon-shaped bundle to consolidate it into a yarn. In the false-twisting, some of the filaments are broken.