This is a freestyle knitted hot water bottle cover/sleeve 😍. Made from bottom up: basically you cast on a number of stitches (divisible by 4 if you want to make the checkerboard pattern, that was 44 in my case) and knit across (I used cable needles) until you reach the narrow upper part of the bottle. Then you start decreasing (alternating with only knit rows so that it isn't too abrupt). The upper part is only knit rows. It's intuitive!