The moisture which has accumulated on the misted glasses is called condensate. Probability of emergence of condensate on the surface of glass depends on temperature difference. It is formed if in warmly, and on the street it is cold.
Remember why morning dew appears – it drops out at big humidity when warm air begins to be cooled. At the same time there is steam which becomes saturated, accumulates on the soil in the form of water droplets. This phenomenon is called dew point when air with certain temperature and relative humidity does not hold moisture in vaporous state any more.
Windows mist over because of the difference of temperatures, this process is influenced also by humidity indoors. This phenomenon is stronger it is observed on glasses in plastic windows. In old wooden frames of glass were located widely spaced. Room glass in wooden double-glazed window manages to heat up more, than the same glass in plastic frame. Because of slots between frame and glass there is natural process of ventilation. Plastic windows are more hermetic, at them condensate will accumulate if indoors there is no ventilation.
Moisture in the normal apartment is emitted from different sources. The humidity is affected also by air temperature. The indicator of relative humidity will exchange during the lowering or rise of temperature, for example, if heating oven. The humidity indoors is higher, the is more abundant condensate will gather. Make simple experiment. Leave per day in the fridge glass bottle. Take out it in the evening and put on windowsill. Droplets will gather for surfaces of bottle. Thus, windows mist over because in the room the humidity has increased and temperature has gone down. For reduction of amount of moisture on glasses it is necessary to lower relative air humidity and to increase temperature. For this purpose provide access of warm air to plain glass. If along saucers there are radiators, and curtains densely close window – lift curtains up or remove them aside. Regularly air the room, providing inflow of fresh dry air.