The time will come when you need or want to substitute a yarn in a pattern. The reasons for this are varied. Perhaps the yarn recommended is discontinued; perhaps it’s too expensive, or perhaps it’s a fiber you don’t wish to use.
Worsted? Bulky? You need to select a yarn in the same weight class. If you don’t, you won’t be able to obtain the correct gauge and your project will not be the correct size. You may eventually be able to obtain the gauge of the pattern but it will be as stiff as cardboard or very loose (depending on if you selected a lighter or heavier weight). For a project such as a sweater, this will have a huge impact.
For a listing of Lion Brand yarns by weight click here.
You can often combine multiple strands of a lighter weight yarn to achieve the same weight as a heavier one. Be sure to check your gauge very, very carefully when doing this. Yarns within the same weight class still work to various gauges. For example, a worsted weight yarn is usually classified as one that works between 16 and 20 sts per 4 inches.
These are approximate equivalents: