I'm not sure if you're asking about a sheath made of ballistic nylon, a nylon fabric formerly used in bulletproof vests, or a ballistic knife, a weapon that throws its blade with a spring in the handle.
There's a recent thread in this forum about ballistic knives. They're illegal in the US, by the way ... I wouldn't know about Poland.
Ballistic nylon is heavier and tougher than cordura nylon ... personally I hate nylon sheaths ... there are some with plastic liners that are more or less usable, though.
-Cougar :{)