The special part of this simple pattern is definitely the yarn - I used Malabrigo Rasta yarn which is gorgeous, beautiful, colorful, and amazing. It's also a super bulky yarn, so you can crochet this cozy in no time at all. Of course, you can substitute any other super bulky yarn that you like.
Using a size L/8.0mm crochet hook, chain 5. Join the stitches into a ring with a slip stitch.
Work 8 DC into the ring. Use a slip stitch to join the first last stitch to the first stitch, completing the ring.
Round 1: CH 2. Work 2 DC into each stitch. Use a slip stitch to join the last stitch to the first stitch.
At this point your crochet circle is just about the perfects size for the bottom of a jar.
Round 2: CH 1. 1SC in each stitch. Join at the end of the round as usual.
Rounds 3-9: Repeat round 2.
Knot off your yarn and weave in the loose ends. You now have a little cozy that looks like this:
The cozy will be very snug, that's ok! We'll be doing a form of blocking that makes the yarn conform perfectly to the shape of the jar. (This way we know that we won't end up with a cozy that's a little too large and falls off all the time!)
Wrestle that slightly-too-small cozy onto the jar:
Run the jar and cozy under your kitchen faucet to dampen the yarn (evenly damp all over, it doesn't have to be soaking, though). Shake off the excess water droplets, leave the cozy on the jar, and place it on your counter or shelf to dry.
Once the cozy is completely dry you will find that it is the perfect size for the jar - snug enough to stay on, but not too tight. It will slip on and off easily.
Enjoy a drink with your new cozy!