First thing, if you haven't checked out Karas Kustoms, you should.
My main appeal to these pens is not just that they look amazing and are high quality, it's the guys behind the curtain making it happen. Being a local Phoenician, I have the privilege of popping by the shop to pick up a pen for myself or a friend wherein I get the opportunity to chat with Bill, Dan, and the crew on their latest projects, business, etc. Seriously, a group of top notch guys that love designing, creating, and manufacturing their own awesome stuff. In house!
This particular Render K is kind of a unicorn. In talking with Dan, the guys were experimenting with various materials and an acetyl plastic called Delrin was one of their choices.
The plastic machined so well and has an extremely smooth finish. It is actually quite amazing how well it did in relation to it's aluminum and brass cousins. Feels great in the hand, and unlike the metal versions, the cap actually posts. This isn't a deal breaker for me at all, but to some people a cap has to post. I believe it is due to the flex in the plastic as opposed to the rigidity of the solid metal. Since the pen is so light, posting the cap adds no uncomfortable weight to the back whatsoever. I didn't get out a scale or anything, but I'd bet the delrin Render K is probably less than half the weight of the aluminum version.
Overall, a great, unique pen from the guys over at Karas that I'm glad to add to my collection!