Ian Waddell wrote:
Does anyone have one of these pads that fixes to the back of your mirror and
keeps it mist free in the bathroom?

http://www.screwfix.com/app/sfd/cat/...02427&id=77859


How effective are they?

The basic idea is that an alternative way of measuring humidity is 'dew point'.
This is the temperature that an object has to be to have condensation form
on it.
It's always lower than (or at) room temperature,
So, if the bathroom is at 28C, and the mirror is heated so that it's at 35C,
there will be no condensation at all on it.