melt-spun fibres extruded through special spinnerets to produce fibres with one or more holes down their length. Such fibres are good insulators and give warmth without adding weight.
Hollow spindle spinning:
a system of yarn formation, also known as wrap spinning, in which the feed stock (sliver or roving) is drafted, and the drafted twistless strand is wrapped with a yarn as it passes through a rotating hollow spindle. The binder or wrapping yarn is mounted on the hollow spindle and is unwound and wrapped around the core by rotation of the spindle. The technique may be used for producing a range of wrap?spun yarns, or fancy yarns, by using feeding different yarn and fibre feedstocks to the hollow spindle at different speeds. Last referenced in: World Markets for Textile Machinery: Part 4--Dyeing and Finishing (Textile Outlook International Issue 143)