Kachera are cotton, drawstring fastened shorts cut to a specific pattern that allows a full range of movement, a design with practical origins in soldiers and horsemen needing underwear that would not restrict them in combat or riding, long before it became a fixed article of faith.
Material and making
Cotton is the standard material, chosen for comfort and practicality rather than any symbolic property, and kachera are made and sold through ordinary tailors and Sikh owned clothing shops rather than requiring any specialist craft, unlike the kirpan or a properly forged kara. Patterns are simple enough that many families sew their own.
Who wears them, and how they are changed
Kachera are worn by baptized Khalsa Sikhs of any gender continuously, day and night, one of the Five Ks, and modesty custom calls for changing into a fresh pair while still wearing another rather than being without one even briefly. Worn out kachera are discarded and replaced like any garment, with no special ritual disposal, the article's significance lying in the constancy of wearing it rather than in the physical garment surviving any particular way.
A style that varies more than the other Five Ks
Unlike the kirpan or kara, which keep a fairly fixed form across regions, kachera style varies more visibly by tailor and community, some cut closer to a swimming short, others looser and longer, and there is no single sanctioned pattern the way there is for the khanda blade. This flexibility reflects the garment's practical origin more than any fixed liturgical design, and a Sikh moving between countries generally finds a locally made pair without difficulty.