Is the aluminum film of the moisture-proof pad facing up or down?

In the propaganda of the manufacturer, it is a very powerful thing that the foam moisture-proof pad is coated with aluminum film. It seems that the thermal value of this layer of aluminum film moisture-proof pad will increase a lot. I have also had similar advertisements, although I have not exaggerated the promotion So, is this aluminum film so powerful? In addition, whether the aluminum film is facing upwards or downwards has also become a big outdoor case.

Let me talk about the principle of the foam moisture-proof pad to keep warm. The foam moisture-proof pad relies on the countless independent small bubbles of the material itself to isolate the heat conduction between the body and the ground. Pay attention to the heat conduction. There are three ways of heat transfer, that is, loss of body heat: conduction, convection, and radiation.

Conduction is the direct heat transfer between two objects with different temperature, that is, if a person is lying on the ground, the person's body temperature will be transferred to the ground. Blocking the conduction of the body temperature to the ground is the core function of the moisture-proof pad.

Convection is the transfer of heat generated by the relative displacement of different parts of the temperature in the fluid. The wind blows away the body temperature to remove the body temperature by convection. The function of the sleeping bag is to block the convection and prevent the air in the sleeping bag from convection with the outside air.

Radiation is the transfer of thermal energy by electromagnetic waves to objects that are not in contact with each other, and the sun that we bask every day is thermal radiation. Radiation from the human body occurs almost all the time, but there is very little heat lost in this way. The role of the aluminum film is to block the heat radiation of the human body.

   

Back to the actual camping environment, the heat loss of the body is blocked by two aspects. One is the cooperation of the tent and the sleeping bag to form an environment with little relative air convection. The air convection is blocked to take away the body heat; the second is the damp pad to block the body and the ground Direct contact to prevent the body from losing heat through heat conduction. The heat radiation of the body is negligible in the actual camping environment.

So is there a layer of aluminum film on the foam moisture-proof pad? hardly.

Because this aluminum film is in the heat conduction system in the entire heat transfer system, the aluminum film cannot block the heat conduction. This can be verified by a very simple experiment. The life blanket is laid on the cold ground, and the person lies down and lies The temperature of the ground can be felt at the moment of going up, which means that the aluminum film can not block the heat conduction, because the heat transferred through the aluminum film is much larger than the aluminum film blocks the heat to be transferred out due to thermal radiation. So there is no need to entangle the moisture-proof pad with that layer of aluminum film, it is just the exaggerated publicity of manufacturers.

By analyzing the principle of heat transfer in the actual camping environment, it can be concluded that if there is a moisture barrier for the aluminum film, the aluminum film should be face down, because the heat conduction effect of the body directly contacting the aluminum film is much greater than the effect of heat insulation and radiation. Only a certain distance between the membrane and the body can play the role of thermal insulation radiation.

In an actual camping environment, how can the best use of aluminum film reflect heat radiation? Put the aluminum film cushion inside the tent, and then light the steam lamp.