The aluminium foil in Isobooster reflects 97% of infrared radiation, but what happens to the other 3%? What actually happens between the various Isobooster layers?
Isobooster consists of several layers of reflective foil with air (a kind of bubble wrap) in between. Most of the air (nitrogen and oxygen) is as ‘invisible’ to heat radiation (infrared) as it is to so-called ‘visible light’ (blue, yellow and red). That means the heat radiation travels straight through it. There are some other gases, including water vapour (H20), through which heat radiation cannot pass. Although these gases make up less than 1% of the air, they have a significant impact on the temperature.
Why water vapour can absorb infrared
The reaction of a gas to radiation depends on the shape of its molecules. A gas molecule can only absorb heat radiation if it can vibrate at the same wavelength as the radiation. (Similar to a tuning fork vibrating at a certain pitch.) In order to absorb heat radiation, the gas molecules must be able to vibrate ‘asymmetrically’. This only happens when gas molecules consist of three atoms or more. Simple, straight molecules consisting of only two atoms, such as oxygen (O2) and nitrogen (N2), cannot do this. Water vapour (H2O), on the other hand, consists of three atoms, which allows it to vibrate and absorb the heat.
Heating up and drying air
As the water vapour molecules absorb heat radiation, the air around it heats up as well. This additional heat is subsequently radiated in all directions and reflected by Isobooster. In between the reflective Isobooster layers, this effect is repeated continuously. As a result, a minimum amount of heat radiation can provide sufficient heating to make the water molecules rise. The air within the Isobooster gradually becomes drier as well. Dry air insulates twice as well as humid air.
In short, the tiny bit of heat radiation which is not reflected by the first layer of aluminium is used effectively to heat up and dry the air between the foil layers. This way, the 3% of ‘escaped’ heat radiation is used to make the thin Isobooster material an even more effective insulator!