Our garage was insulated before the mice moved in. We used proper roof insulation that is like a foam board covered in silver foil. I have just asked Dave how much it would cost to buy now and the answer was about £26 a sheet :shock: The sheets weren't that big either, so it would be expensive for most people to use this method. However, polystyrene and bubblewrap would also work, if you can get hold of any. Even putting curtains or old sheets etc up at the windows might help slow the heat transfer. It depends on what kind of garage you have I suppose, ours is brick built and separate from the house, with an up and over garage door at one end where the car is supposed to drive in (never used it though). This door has been covered over with bubblewrap stapled to the door frame! It is 20ft by 10ft so quite a big space.