Crystal Clear Aqua Balloon - perfectly round, stretchy long neck.

For this 330mm Aqua balloon, the minimum recommended filling size is 380mm and the maximum filling size is 600mm. The balloon can be filled with air or helium and should be inflated with a fast inflating speed, to prevent the balloon from losing its left-right balance and becoming misshapen.

Instructions on inflation - https://www.youtube.com/watch?v=bqCgyyOVV4k&feature=youtu.be