It's basically made in the same way as a slip on cushion cover. I used some leopard print fabric which was pretty thin so to help absorb some of the heat from the hot water bottle, I cut up a fluffy old dressing gown that wasn't in good enough nick to donate to the charity shop. Anyway, enough of the waffle, here's how you make it:
Step 1. Draw out your template
Trace around your hot water bottle. Then cut it out leaving a good 1" seam allowance.
Step 2. Cut out your fabric pieces
The front will be one whole piece.
The back will be made of two separate pieces. The bottom 3/4 of the template and the top 1/3. When laid against the front cover piece they should overlap one another.
*I overlocked the top of the bottom piece and the bottom of the top piece, but this isn't necessary. You could simply stitch them over or tidy them by adding bias binding.
Step. 3 Stitch together
With right sides together, pin the three pieces together so that the back bottom piece, overlaps the back top piece, (see image below). Pin in place and then stitch all the way around.
*At this point you may find it useful to tidy the edges up a little if, like mine, they were a bit of a mess.
Once the cover is all stitched together, turn inside out (so the right sides are facing out) and admire your handy work. At this point I also added an iron-on patch to try and lesson the Bette Lynch effect I had created.