For this test, which is only to evaluate and get the correct measurement,volume and data, we use a simple Pilates ball,  some pneumatic couplings and various plastic containers with different volumes to see how much space the balloon will need in the rocket.
Fun as it is, The pilates ball we use turned out to be large enough in order to use in the rocket. It contains about 220 liters of Co2, 750mm diam, and it can withstand a external pressure up to 200 kg.

All sections of the rocket will be equipped with a flotation system to ensure that they are kept afloat after landing.