The 'hollow' cords are plastic tubing and they may or may not be soft and flexible, but will be thick which can be a problem moving your stitches on them. The metal may be flexible don't know. It may be worth it to just get a couple of each type to see how you like them. Or one of the sample sets from Knitpicks or WEBS (www.yarn.com
) Knit pro needles.