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This very thin recycled cashmere can be doubled or tripled to be

If you want to knit something, but you don’t have the yarn the pattern calls for or you can’t afford the yarn, you can substitute. Be careful! One yarn isn’t always the same as another.

You need to figure out the weights of the yarns in question. How many WPI (wraps per inch)? This is figured out by wrapping a piece of yarn around a ruler. Depending on the number of wraps in an inch, you can figure out if the yarn is worsted weight, sport weight, fingerling, lace or bulky......

Read more at -  http://www.examiner.com/x-7054-Baltimore-Knitting-Examiner~y2009m7d9-Substituting-yarn