If you're looking to create a thicker, bulkier yarn from a fine-weight yarn, here's a simple technique to help you do just that using only one strand.

Start by laying your fine yarn out in an S shape. Once you've done that, pick up the yarn at the end where your S shape began, gather all three strands together, and tie a slip knot onto your crochet hook. From here, you can begin crocheting with all three strands at once.

As your three strands start to run out, you’ll be left with a loop and a single strand still attached to your working yarn. To extend your project, simply pull that single strand through the loop, and add more yarn by pulling out another length of yarn. Continue crocheting as you would normally.

Whenever your three strands run out, just repeat the process—pull the single strand through the loop and continue crocheting.

And that’s it! From one fine strand of yarn, you can create a lovely thick, bulky weight yarn.