Phlogiston is able to store more energy than its surrounding matter. When heated to around 1000°C, it will rapidly increase in volume and release luminous and thermal energy. This is macroscopically described as "burning". It will then fill the air around it, which prevents burning. It cannot burn when in direct contact with a humour.
One can create a fire-proof room by saturating the air with phlogiston. Ocean water is naturally saturated with phlogiston, which is why it usually does not burn. It rarely crosses the chemocline between different humours.
This aether is invisible when not excited. It has a very faint smell.