Probably a pretty basic question, but is a little confusing to me. I am trying to make a 100% cashmere dress. The pattern calls for Anny Blatt Capella yarn and is listed as a #5 on the Yarn weight system. I decided because I have priced this yarn at my favorite store at $41.00 for a 25g ball that I would do some shopping around and try to substitute the yarn out with a less expensive brand but am trying to figure out how to do that. A couple of the people selling yarn on line have listed the yarn as 1ply, 2 ply, 12 ply etc. What does that mean and how can I make sure I am getting yarn comparable to what I need. Thanks for your help.