I have produced more hot water bottle patterns than anything else, having spent the best part of two years supplying hand knitted hot water bottles to John Lewis. This one is in 4 ply, which is quite unusual. The original was knitted in RYC cotton cashmere 4 ply, which is now discontinued (you might be able to find some online), but Sublime Merino Cashmere 4 ply will work equally well, as will Rowan pure wool 4 ply.

I recently re-designed the pattern in Artesano 4 ply for KnitCrate, and the photos of the grey version are in this yarn. It works brilliantly. There is a heart motif, which is knitted using the Intarsia technique. You only need one ball of 4 ply and oddments in the contrasting colour. The pattern is for a ONE litre hot water bottle (smaller size).

UPDATE: Now with a free pattern for a lovely lavender pouch! You can make this pouch using the rest of the yarn from your second contrasting ball of yarn, meaning that you have no wastage, and it just smells SO good!

To make the lavender pouch you need about 30gs of 4 ply yarn in one colour and 5gs in another colour. (You will have enough from your two balls of yarn if you have knitted the hot water bottle first, reversing the colour scheme). You also need an 80cm length of velvet ribbon, a 20cm x 11cm piece of muslin or thin cotton material for the lining bag, and 20gs of dried lavender flowers (You can usually get these from a health food shop).

This pattern was available as a kit from KnitCrate. (Note that the kit includes the pattern, a 0.8L bottle, and the required yarn.