I use a hot water bottle almost every night (this includes summer), but somehow had never gotten around to knitting it a cover. Last night I was trying to go to sleep early, but at 11 decided I absolutely MUST knit a cover NOW, before anything else can take place. So I stayed up and knit a hot water bottle cover. It's a really loose knit, because that's all I had on hand, but I sort of like it - gives me the imression the heat will escape better. In any case, I totally love it and it is now snug in my bed.