Plastic knitting needles are lightweight, smooth, and flexible. They are warm in the
hands because they assume your body temperature after a bit of knitting. Their flexibility
means that they are subject to warping. This may or may not bother you.
Some plastic needles made by the Pony Company have a flexible metal core running
through them to strengthen them. This was done because older plastic knitting needles did
tend to break, especially the thinner ones.
Bryspun makes a white plastic needle that has a concave tip that some people like
for its ability to grab stitches effectively. This tip works well for some yarns,
but tends to split other yarns, in my experience.
Some plastic needles come in great colors. Pony Pearls come in iridescent
marbleized pastel colors. Online auctions sometimes offer vintage
Australian needles made by Patons in beautiful, bright primary colors. I just want to warn
you that the thinner ones do break. I found this out by personal experience, unfortunately.
However, they are just gorgeous needles and have wonderful tops, so you may want
to indulge your collecting habit by getting some. Just avoid sizes 0 through 3.
A final word: Plastic knitting needles are probably what you want to get if you do a lot
of knitting with really big needles. From size 11 on up, most of us prefer plastic needles
because they are so much lighter than others.