The yarn is worsted weight acrylic. The purple is Red Heart With Love Boysenberry. The tan and green I think are Loops and Thread Impeccable Soft Taupe and Fern. I used an H hook.
Here's what I did in brief.
Size: fits a Dasani 16 oz water bottle as shown
Materials: H hook and small amount worsted weight yarn.
Rnd 1: work 12 dc in an adjustable ring, join to first dc with sl st
Rnd 2: ch 1, 2 dc in same stitch, 2 dc in each remaining dc. Join to first dc with sl st. (24 dc)
This came out to be about 2 1/2". It will be easier to sew the beginning tail in now.
Rnd 3 - end: ch 1, dc in same stitch, then work even (dc in each dc around). Join to first dc with sl st. (24 dc)
Finish off. I use the invisible finish off and then weave the tail in.
For the green (tallest) cozy I worked 15 rounds. For the tan I worked 13. For the boysenberry I worked 11.
As seen in the photo below, the tallest is about 6", the middle 5" and the smallest 4". That is with keeping the bottom flat. Size would depend, of course, on your tension, your hook, your yarn.
To adjust size you can use different yarn, a different number of rows or a different size hook.
Some like to make them using single crochet. That would give a tighter weave. You'd need to make adjustments to do that, of course. Shorter stitch requires fewer beginning stitches in the first round, more rounds to get to height etc.