What is the working principle of the self inflatable mat used in the field

The principle of automatic inflation of the self inflatable mat product is to close the open air chamber in a waterproof nylon shell, and it will automatically expand when used.
Automatically inflatable cushions generally have a built-in high-resilience full-fat sponge, and the specific principles are as follows:
The air cushion has a built-in high-resilient full-fat sponge, and the air valve is opened. The rebound of the filling similar to the sea surface makes the self inflatable mat absorb air; after the valve is closed, the air is enclosed in the air cushion. Since the packaging is compressed by the machine when it leaves the factory, the first inflation will be slower, and the effect will be better if you use it several times or fold it several times.
Extended information:
Precautions for the use of self inflatable mat:
1. Do not approach sharp objects (thorny plants or sharp stones or blades).
2. When the tent is not in use, please spread a base cloth under the air bed.
3. Do not use it as a float.
4. Keep away from flames or sparks.
5. When the temperature is high, do not place the inflated air bed with the valve closed in the car or tent.
6. Do not stick to sunscreen oil or alkaline medicines.
7. Do not expose to the sun for a long time, ultraviolet rays will slowly damage the surface material.
8. Please place it out of the reach of pets.
9. The gas nozzle is hard, so you should avoid it when you are resting.