Acupuncture Needle Head

Chinese Medicine has a range of needles that they use. The vast majority of practitioners use stainless steel needles for most of their patients. There are, however, gold needles, zinc needles, copper needles and then the "Japanese" style needles which often have a plastic handle and may or may not have a silicon coating on the needle for a smoother insertion.

Practitioners have their own preferences, but within Japanese acupuncture you are often using needles with different metals to create different polarities within the body.

As far as touch or sensitivity goes, I think you can feel what you need to feel through any needle type particularly with practice. Obviously plastic needles do not allow energy to travel through as a metal conduit would so there are some differences, but within Japanese acupuncture they use plastic needles regularly with some of the more specific and sensitive needling techniques.

For polarities you should read the following article on the use of magnets in Japanese Acupuncture (it has the list of polarities for the common metals):

Magnet Therapy - Japanese

For most TCM practitioners it comes down to using stainless steel or copper and there have been little studies done on the clinical differences between the two. There is only one study that I could find that showed copper needles creating more positive changes than the stainless steel needles. I wouldn't base too much on one study, however.