In general, natural fibers tend to require more careful handling than synthetics because they can shrink, felt, stain, shed, fade, stretch, wrinkle, or be eaten by moths more readily, unless special treatments such as mercerization or superwashing are performed to strengthen, fix color, or otherwise enhance the fiber's own properties.
Protein yarns (i.e., hair, silk, feathers) may also be irritating to some people, causing contact dermatitis, hives, wheezing,
or other reactions. Plant fibers tend to be better tolerated by people
with sensitivities to the protein yarns, and allergists may suggest
using them or synthetics instead to prevent symptoms. Some people find
that they can tolerate organically grown and processed versions of
protein fibers, possibly because organic processing standards preclude
the use of chemicals that may irritate the skin.
When natural hair-type fibers are burned, they tend to singe and have
a smell of burnt hair; this is because many, as human hair, are
protein-derived. Cotton and viscose (rayon)yarns burn as a wick.
Synthetic yarns generally tend to melt though some synthetics are
inherently flame-retardant. Noting how an unidentified fiber strand
burns and smells can assist in determining if it is natural or
synthetic, and what the fiber content is.
Both synthetic and natural yarns can pill. Pilling is a function of fiber content, spinning method, twist, and fabric construction.
Yarns combining synthetic and natural fibers inherit the properties
of each parent, according to the proportional composition. Synthetics
are added to lower cost, increase durability, add unusual color or
visual effects, provide machine washability and stain resistance, reduce
heat retention or lighten garment weight.
