I got a water bottle at work.
It was not insulated.
I fixed that.
Yarn: Lamb's Price worsted, hyachinth (the bright purple). Louet Gems Topaz (worsted), grape heather.
Needles: Addi Turbo US#6.
Pattern: I don't need no stinkin' pattern, at least for something as simple as this. First I knit a 2x2 ribbed sleeve of the light purple yarn, ~28 stitches. That didn't seem thick enough, so I continued with the bright purple and added some stripes. Easy peasy.
Sadly, it doesn't insulate as well as I had hoped. But it helps.
