A proper ventilation ensures a breathable air inside.
The inner tent, in the case of the 2 pieces, is made from a material that allows air to circulate. Also, most models have an insect net on the top in order to ensure that the air can easily cross without allowing the insects get in.
The air from the space between the inner tent and outer foil is refreshed by the air that enters under the outer foil and the vents cutted in the outer foil.
A ventilation system of high quality ensures the maintenance of a pleasant air, avoid condensation, without air flow. Models that have insect nets on the side and cannot be closed, the air flow can be created during a stronger wind. It’s good that before buying to check the layout for insect nets, by viewing a picture of the inner tent (without the outer foil being installed).
Products of 2 seasons, have a very large insect nets, in order to ensure a highly proper ventilation. At the other extreme, are the 4 seasons tents, where the mesh may be missing and ventilation under the outer foil is blocked by a sleeve. In the case of 3 seasons models, most suitable in most cases, the mesh is , generally, in the upper area of the inner tent and possibly in front of the entrances. It is important that the insect nets can be closed with a zipper on the inner tent (nylon or polyester) in order to keep the warmth inside when it’s cold outside or when the wind blows.
In summer, the best ventilation is provided during the day at models with 2 entrances. Such a model which has two entrances is recommended especially in summer.