i just realized that the name Invisafil might make it sound like a clear monofilament poly. As BellaBoo commented, it behaves much like silk. It's an opaque thread but so fine and matte that it seems less noticeable than the monofilaments, and it won't feel scratchy. I think it's great stuff.
--Heidi
http://www.hugstitches.com
http://www.flickr.com/photos/32113973@N05/