How to properly insulate a bathroom with 2 walls been concrete blocks?
I'm about 2 hours south of you. Cut 1/2" styrofoam between those strips, use a wide flashing tape to cover the furring strips and lap over onto each piece of stryofoam to the left &amp; right of the furring strip.

Then, Keep gettin up. Put you some good 1/2" material on the wall, for the sake of your tile. I suggest cement board, but you'll do what you prefer.

The difference between what I just suggested, and 2" of foam, will make no difference in perceived heat loss, or electric bill increase.