2012 mini convertible here. My dash and side windows are ALWAYS covered in fog, to the point where it is dangerous to drive because I can't see. The de-fogger button does nothing and I really hate using the AC in the cold winter!! Any advice?

 

You're not going to like this - use the AC. Just be glad you haven't got a Roadster (even smaller interior, so fogs up even quicker).

Making sure the heater is not on recirculate is important - as is cleaning the inside of the windows and then not touching them with anything.

Also, are all the carpets (and the floor beneath them) dry? If you have got water inside the car, nothing will stop it fogging up. Worst case is that you might have a seal gone somewhere, letting in moisture.

 

AC is a must in the winter. Air conditioners remove humidity from the air, thus less fog.

MINI's automatic climate control system keeps the AC on all the time regardless of temperature, at least it does on my roadster.

 

Bright sunny day, 18°, hat, coat and gloves, top down - no fog.
Join the 'how cold is it' crowd and build a reputation.

 

But you can switch the AC off after pressing the auto button, leaving the rest of the system in auto. Any time you press the auto button again, it also switches on the AC again.

 

Try putting Rain-X Anti-Fog on your windows to see if that makes a difference. I've used it with success before.

 

+1 on the ac, you might also nee the clean the front windshield on the inside, they can get a film on them and when you get a fog buildup its worse. The rain X Anti fog works somewhat but you have to keep redoing it.