I thought about having a chemical that releases gas when it comes into contact with water to inflate a float, of course all these things add, weight and drag.
Whilst thinking about this I looked up Sodium Bicarbonate which people take for upset stomachs. It seems the recommended dose is safe but research showed that most people went way beyond a half-teaspoon and ;
Some people selected doses of bicarbonate that would result in several hundred milliliters of gas release within 3 min; it seems likely that such injudicious ingestion of sodium bicarbonate, if taken when the stomach was distended with air, food, and liquid, could be an important factor in spontaneous gastric rupture.
Good grief!