Editing Silk (section)

===Physical properties===
Silk fibers from the ''Bombyx mori'' silkworm have a [[triangle|triangular]] [[cross section (geometry)|cross section]] with rounded corners, 5–10&nbsp;[[μm]] wide. The fibroin-heavy chain is composed mostly of [[beta-sheet]]s, due to a 59-mer amino acid repeat sequence with some variations.<ref name=lewin2007>{{cite book |editor1-last=Lewin |editor1-first=Menachem |title=Handbook of fiber chemistry |date=2007 |publisher=CRC/Taylor & Francis |location=Boca Raton |pages=438–441 |isbn=9780824725655 |edition=3rd}}</ref> The flat surfaces of the fibrils reflect [[light]] at many angles, giving silk a natural sheen. The cross-section from other silkworms can vary in shape and diameter: crescent-like for ''Anaphe'' and elongated wedge for ''tussah''. Silkworm fibers are naturally extruded from two silkworm glands as a pair of primary filaments (brin), which are stuck together, with sericin proteins that act like [[glue]], to form a [[bave]].<ref>{{cite book |last1=Burnham |first1=Dorothy K. |title=Warp and weft : a textile terminology |date=1980 |publisher=Toronto : Royal Ontario Museum |page=3 |isbn=978-0-88854-256-4}}</ref> Bave diameters for tussah silk can reach 65&nbsp;μm. See cited reference for cross-sectional SEM photographs.<ref name=lewin2007 />

[[File:Silk raw 01a.jpg|thumb|left|Raw silk of domesticated silk worms, showing its natural shine]]
Silk has a smooth, soft texture that is not slippery, unlike many [[synthetic fiber]]s.

Silk is one of the strongest natural fibers, but it loses up to 20% of its strength when wet. It has a good [[moisture regain]] of 11%. Its [[Elasticity (physics)|elasticity]] is moderate to poor: if elongated even a small amount, it remains stretched. It can be weakened if exposed to too much sunlight. It may also be attacked by insects, especially if left dirty.

One example of the durable nature of silk over other fabrics is demonstrated by the recovery in 1840 of silk garments from a [[HMS Royal George (1756)|wreck of 1782]]: 'The most durable article found has been silk; for besides pieces of cloaks and lace, a pair of black satin breeches, and a large satin waistcoat with flaps, were got up, of which the silk was perfect, but the lining entirely gone ... from the thread giving way ... No articles of dress of woollen cloth have yet been found.'<ref>''The Times'', London, article CS117993292, 12 October 1840.</ref>

Silk is a poor conductor of [[electricity]] and thus susceptible to [[static cling]].  Silk has a high emissivity for infrared light, making it feel cool to the touch.<ref>{{cite news|last1=Venere|first1=Emil|title=Silk fibers could be high-tech 'natural metamaterials'|url=https://phys.org/news/2018-01-silk-fibers-high-tech-natural-metamaterials.html|access-date=2 February 2018|work=[[Phys.org]]|date=31 January 2018|archive-date=1 February 2018|archive-url=https://web.archive.org/web/20180201185150/https://phys.org/news/2018-01-silk-fibers-high-tech-natural-metamaterials.html|url-status=live}}</ref>

Unwashed silk chiffon may [[shrinkage (fabric)|shrink]] up to 8% due to a relaxation of the fiber macrostructure, so silk should either be washed prior to garment construction, or [[dry cleaning|dry cleaned]]. Dry cleaning may still shrink the chiffon up to 4%. Occasionally, this shrinkage can be reversed by a gentle steaming with a press cloth. There is almost no gradual shrinkage nor shrinkage due to molecular-level deformation.

Natural and synthetic silk is known to manifest [[piezoelectricity|piezoelectric]] properties in proteins, probably due to its molecular structure.<ref>{{cite web |url=http://fs.tx.ncsu.edu/Past_Meetings/Spring_2003_Loughborough/papers/081-Ellison.pdf|title=Piezoelectricity in Natural and Synthetic Silks|access-date=28 April 2010|url-status=live|archive-url=https://web.archive.org/web/20110720011853/http://fs.tx.ncsu.edu/Past_Meetings/Spring_2003_Loughborough/papers/081-Ellison.pdf|archive-date=20 July 2011}}</ref>

Silkworm silk was used as the standard for the [[denier (measure)|denier]], a measurement of [[linear density]] in fibers. Silkworm silk therefore has a linear density of approximately 1 den, or 1.1 [[dtex]].
{|class="wikitable"
|-
! Comparison of silk fibers<ref>{{cite web |url=http://web.mit.edu/course/3/3.064/www/slides/Ko_spider_silk.pdf |title=Engineering Properties of Spider Silk |author=Ko, Frank K. |author2=Kawabata, Sueo |author3=Inoue, Mari |author4=Niwa, Masako |access-date=9 July 2010 |url-status=live |archive-url=https://web.archive.org/web/20100331215511/http://web.mit.edu/course/3/3.064/www/slides/Ko_spider_silk.pdf |archive-date=31 March 2010}}</ref>!! Linear density (dtex) !! Diameter (μm) !! Coeff. variation
|-
|[[Moth]]: ''[[Bombyx mori]]''||1.17||12.9||24.8%
|-
|[[Spider]]: ''[[Argiope aurantia]]''||0.14||3.57||14.8%
|}