A very easy balloon to make. You can use as many bags as you want - so you can create a tube small enough for the backyard, or a giant one that will fill a field.
In these instructions, I'll use 8 bags as an example.
Supplies:
Hefty Basics 30 gal. black bags OR 0.4 MIL 30 gal. Ruffies bags
Roll of masking tape, scotch tape or any lightweight tape
Scissors
Instructions:
Do not cut open the bags. Only cut the seams off.
Tape the open ends together, using at least a half-inch overlap. Continue this until all the bags are sealed together to form a long tube.
Seal one of the open ends completely. Then invert the entire balloon like a sock.