If you want a sheath for field use, compared to Cordura or leather, Kydex offers better protection for your knife, is usually smaller overall, doesn’t soak up water or snow, and cleans easier. All my field knives wear Kydex, specifically Rainwalker.

But there’s nothing like a good leather sheath for beauty. They’re not as good in the field as Kydex, but you can’t beat them for looks. Leather is also the most expensive.

The other major sheath material is Cordura, which is plain looking and less functional than Kydex but usually the cheapest.

To summarize: Kydex for use, leather for show, Cordura for price.