Kasavu is a technique used in handlooms of Kerala, that very fine threads of gold or silver used in weave to make border lines and designs on silk and cotton fabricshandloom. This technique later spread to most of India and Kasav technique developed many other fabrics across India. White or off-white cotton cloth with Kasav borders that originated in the South Indian state of Kerala is now famous as Kerala saree is believed to be first form of use of Kasav technique.
The original kasavu was made by hand from fine golden or silver threads to make border lines or designs on cotton or silk fabrics. It is believed to date back to the Buddhist era and continues to be worn by Malayalis, the residents of Kerala. It is worn by both women and men, especially during festivals, dances, and special occasions such as weddings and piranna naal (birthdays according to the local calendar.) During the Vishu festival, it is customary to place a brand new kasavu cloth near the traditional Vishukkani (lamp) as a symbol of wealth and prosperity. During dance performances such as the Mohiniyattam (dance of Vishnu in female form), only kasavu garments are worn by participants. Dances such as Kaikottikali or Thiruvathirakali  (dance of clapping) also have women performers wearing kasavu sarees and traditional red blouses. Generally Kaikottikali is performed by 8–10 women, but can include more participants; the world record for the largest number of Kaikottikali performers is 2643 women at a time!
Traditionally Kasav was gold or silver threads but as it is expensive is not used now. Now typical white or off-white garments with a gold or silver coloured border is considered traditional and is called Kerala saree or Kerala Mundu.Garments made with kasavu are long, rectangular pieces cloth called the mundu, wrapped around the lower body, and the veshti, wrapped around the upper body. Women typically wear a red, green or gold traditional blouse under the veshti while men sometimes wear a formal shirt.
The cost of a "kasavu set" or "kasavu settu" comprising the mundu and veshti varies according to the width of the gold borders. Borders can range from 3/4" or less, to 6" or more in width.
Though originally from Kerala, over time kasavu has spread across India, especially to the adjoining south Indian states of Tamil Nadu, Karnataka, Andhra Pradesh, and Telangana. In Kerala, there are villages devoted entirely to the manufacture of kasavu cloth. Notable among them is the village of Kuthampully near Ottapalam, which lies between Thrissur and Palakkad. The Devanga chettiar community of weavers in Kuthampully were brought from Karnataka by the Maharaja of Kochin 500 years back. The entire village population create kasavu cloth, pool their produce together, and sell it through a centralized, collective market.
The traditional mundu-veshti  has evolved over time and women prefer to wear a single-piece saree rather than the original two-piece garment. Also, the original garments had pure gold borders, whereas the newer versions have red, green, orange etc. colors along with gold, to make them look more attractive. Powerlooms are also replacing handlooms but the machine-made fabric differs in texture from the original, though they are cheaper to produce on a mass scale.
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- "Kerala Kasavu". external.