Legionella enters the body mainly by inhaling aerosols (mist) containing bacteria. In an exterior hot tub, when the water is stirred, a large amount of water mist is produced, and people may inhale these bacteria during breathing. If there are too many Legionella in the hot tub water, inhalation may cause Legionnaires' disease.

Polyurethane foam is one of the most common hot tub insulation materials on the market. It is favored for its excellent insulation performance and wide application. The closed-cell structure of polyurethane foam effectively reduces the loss of heat from the exterior hot tub through convection and heat conduction, so it can significantly reduce energy consumption.