1. When a filled balloon and an unfilled balloon fall on the Earth, both are subjected to gravity and buoyancy force.
2. The buoyance force is dependent of the surface area as it is created by the amount of air displaced by the object.
3. Since the buoyancy force for unfilled balloon is small, it is not much resisted and falls freely while filled balloon has similar mass but has large surface area so buoyancy is of applicable amount and it is lifted up before falling slowly on floor.