That was what I was asked for when I offered to make a hot water bottle cover for my favourite 13 year old. And this is what I came up with…

Made in Drops Alaska Dark blue (37), Navy blue (12), Denim blue (57) and Mustard (58) on a 6mm hook. Hiding behind it is another basket-weave bottle cover in Drops Karisma Grape (83)
The cover is made in two-row stripes of UK double crochet and is 28 stitches wide over the bottle, and 16 stitches wide over the neck. I had two goes at this to make the stripes work and my final version was 20 stripes long for the back section, then 15 and 7 stripes long for the front sections. The neck sections are 6 stripes long.
The main front, back and neck sections all start with Dark blue (12) and the top front section starts with Denim blue (57). The pieces are joined together with Navy blue (12) using UK half treble crochet.