Byssus cloth

Sea silk is an extremely fine, rare, and valuable fabric that is made from the long silky filaments or byssus secreted by a gland in the foot of pen shells (in particular Pinna nobilis). The byssus is used by the clam to attach itself to the sea bed.

Sea silk was produced in the Mediterranean region from the large marine bivalve mollusc Pinna nobilis until early in the 20th century. The shell, which is sometimes almost a metre long, adheres itself to rocks with a tuft of very strong thin fibres, pointed end down, in the intertidal zone. These byssus or filaments (which can be up to 6 cm long) are spun and, when treated with lemon juice, turn a golden colour, which never fades.

The cloth produced from these filaments can be woven even finer than silk, and is extremely light and warm; however, it attracts clothes moths, the larvae of which will eat it. It was said that a pair of women's gloves made from the fabric could fit into half a walnut shell and a pair of stockings in a snuffbox. In addition, Pinna nobilis is also sometimes gathered for its flesh (as food) and occasionally has pearls of fair quality.

The Greek text of the (196 BCE) Rosetta Stone records that Ptolemy V reduced taxes on priests, including one paid in byssus cloth. This is thought to be fine linen cloth, not sea silk. In Ancient Egyptian burial customs, byssus was used to wrap mummies; this was also linen and not sea silk.

The sophist author Alciphron first records "sea wool" in his (c. 2nd century CE) "Galenus to Cryton" letter.

...
Wikipedia