you can use helium if you want to make the balloon float, otherwise the air is better.
If you can, you should keep them carefully. I put the arch together at night and took it in a van to the party place, and there I finished fixing it or putting more balloons adapted to the space. Lucky
It takes about an hour with an air pump for balloons.
They last a week and some last even longer. The bigger the balloon, the longer it takes to deflate.
The length of the balloon strip can be decided according to the number of balloons you tie, you can use the whimsy to tie any different length of the balloon arch.
Pull the balloon knots into the balloon strip holes, then fill the gap with the 5" balloon with balloon glue, and finally put the 18" balloon at the end.