Fill ’em up! The first Friday in August ushers in National Water Balloon Day just in time for the hottest days of summer! Pop, throw, splash, or just squish! What kid or adult doesn’t enjoy a water balloon in the hot summer? Since Edgar Ellington invented the waterproof sock in 1950, backyards haven’t been the same. Whether kids compete or take up sides in a good old water balloon fight, the cool, wet fun lasts all summer long. Filling a blue balloon with water! Summer lifestyle!