Hello Paulina. I use blankets at night, and on very cold days keep three sides and the top covered with them.

I put heavy towels around the window sill when it's really cold. It stops cold air from coming in, in case the insulation isn't what it should be.

BUT, it makes it pretty dark in the cage, so at night I leave a couple corners pulled open just a little bit to let in fresh air and a little bit of light.

Good luck on this. I've never used a heating pad but it sounds like a good idea. KKsuns and BLR know what they're talking about!

Dinah, Tweetymom

RIP precious Merlin
RIP Tweetylove
Rest with Merlin