Part of the typical open-chamber foam is put into an expandable nylon envelope, which can be improved: first, it can be waterproof and can adjust the air pressure, so it is more elastic than a closed-chamber sleeping pad.
Inflatable foam room sleeping pads are warmer than ordinary flat air mattresses because of the addition of Nylon. Because it minimizes air convection and reduces heat loss.
The manufacturing process of the closed-chamber foam sleeping pad is quite simple: pour or press the foamed plastic into the mold, and then cut it into the final shape. Some closed-chamber foam sleeping pads also add a layer of open-chamber foam to increase softness; but this layer of open-chamber foam will absorb water, which will make your sleeping bag wet.
As for the price, the closed-chamber foam sleeping pad is about three-thirds to one-fourth of the open-chamber foam sleeping pad.