Knives that come with a Kydex sheath
Kydex is a trade name that SEKISUI KYDEX lists among its registered trademarks: a family of proprietary thermoplastic sheet grades the company says can be heated, formed and finished into durable parts. On a knife listing, Kydex sheath is the knife maker's or the supplier's word for the sheath's material.
SEKISUI KYDEX's site lists KYDEX among the "registered trademarks of SEKISUI KYDEX, LLC," describes KYDEX thermoplastics as "proprietary, high-performance thermoplastic sheet materials manufactured by SEKISUI KYDEX" and calls itself "the sole manufacturer of authentic KYDEX" sheet. Its history page traces the brand: KYDEX 100 was invented in 1965 near Philadelphia at the Rohm & Haas Co., former Rohm & Haas employees bought the production assets and the brand name in 1987 and started the Kleerdex Company, and SEKISUI Chemical acquired that company in 1990. The suggested applications on its data sheets include aircraft interiors, mass transit vehicle interior components and equipment housings.
The knife makers' lines about a Kydex sheath are brief. CIVIVI's spec lines read "Sheath: Black Kydex Sheath" with no description, and Buck's 2026 catalog lists "Black Kydex sheath with belt attachment, imported" in some fixed-blade entries. Kershaw says the Pack Mule's "custom-fit Kydex sheath" offers "built-in retention" and lists it with a "retention strap and drainage hole."
None of those pages names SEKISUI or a KYDEX grade, and the product data's sheath lines do not either, so a listing's Kydex sheath names the material as its maker or supplier words it; whose sheet and which grade are for the knife's maker to say. How Kydex sits beside leather and nylon, as the makers describe each, is laid out in leather, nylon or Kydex sheaths, and the sheath's safety role is covered in the safest way to carry a fixed blade.