Bulky yarn is made from air-formed polyester silk and is not twisted. Therefore it is softer than normal yarn. Even when used for stretchable seams, the individual fibers are not stretchable on their own. The stretchability comes from the crimping of the individual threads and the bunching up. Due to its fibrous, soft structure, bulky yarn lies much nicer when sewing. Cover seams in particular are effective and flexible with the bulky yarn.
Bulky yarn is preferred for sewing highly elastic fabrics, e.g. in sportswear and underwear. Due to its high opacity, bulky yarn can also be used for rolled hems and/or appliqués, as the seam is very soft and visually stands out more.
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