The term 'TYPE OF BALLOON' can be summarized by two crossword solutions: LEAD (4 letters) and HOTAIR (6 letters). LEAD balloons are a type of balloon that is filled with a gas heavier than air, such as carbon dioxide or sulfur hexafluoride, and are used for scientific experiments. Hot air balloons are a type of balloon that is filled with heated air and is used for recreational purposes, such as sightseeing.