We've had more than one hot water bottle fail and it's resulted in one case in a soaked bed, which was unpleasant and difficult to deal with. I much prefer the

We've had more than one hot water bottle fail and it's resulted in one case in a soaked bed, which was unpleasant and difficult to deal with. I much prefer the failure mode of "catches fire in the microwave". The fire is small (and mostly just a smouldering edge of fabric), easily contained, easily put out, and the failure is easily avoided. We've used both and settled on the wheat bag, but I recognise that other people will make other choices, and that's fine.