The LILIPUT ballpoint from Kaweco, made of stainless steel, is particularly sustainable.  It is made entirely in Germany and thus goes through very short transport routes.
 
Measuring a total length of just 98mm and including a high-quality cardioid curve mechanism, it sets itself apart from other ballpoints as a particularly precise and quiet writing instrument.
 
The body, made of high-quality stainless steel, gives this ball pen exceptional haptics and elegance.

The pen includes a blue 1mm refill that slides easily on paper.