This tri-shutter card (pictured here closed) fits inside a regular envelope. I took a 5.5" x 12" piece of CS, scored at 2", 4", 8", and 10". Then I cut 1.5" in on the top and bottom from the first score line to the last. Then decorate!
I used scraps of leftover Bella Rose scrapbooking paper to decorate! Added "wow" with a build-a-brad on the front and paper piercing on the inside.