Duct is fine for protected skin, that is, if the person to be bound is wearing long sleeves and long socks/pants then it won't damage skin/hair. You can use vetwrap/ace bandages to protect the face and hair if you want to use the tape for a gag.
If you dont want to protect the hair and skin, stick (see what I did there) with medical tape and gaffing tape to avoid making the "unwrapping" unpleasant.
Male, 29, with a preference for ropes, tape, and cloth. I like to do the tying and am only interested in non-sexual bondage. If you'd like to chat, send me a private message sometime! My avatar is the work of nightwrap79 (deviantart).[/url]
Duct tape works great, but gauze and other medical tapes don't seem to leave as much irritation afterwards. It's my understanding that bondage tape is teflon and while expensive, it's definitely worth using.