Derlin is a really strong plastic used to make more solid parts, like gears for RC helis. Similar to Acrylic in that respect but resistances to different chemicals than acrylic. The difference between either and a bic pen tube is quite a bit.
I can actually smell certain grades of stainless steel, if that makes sense, it's weird. Specially a freshly sanded piece of steel, something about the metal in it, I can just sense it. It doesn't bother me though.
I don't use my aluminum tips anymore because of the skin-collecting quality mentioned. I will still give steel a try when I get my PT2