ivillage (NBC Universal's parenting website) recycled the Balloon Racers piece from this past summer (page 6) for a piece on reusing cardboard for fun. It's nice to have new viewers to the blog. They link to the preschool tag, so you have to scroll a bit to get to the balloon racers we did in April 2012.
Here's a better link if you are looking for instructions: balloon racers.
Enjoy your racing!