Figure 4. Top, the two helmets with compressed paper fiber bowls inserted into them. This was done because a thermal imager works by converting infrared radiation (heat) emitted by an object into the visible spectrum. Basically the instrument measures the temperature as a function of the images ‘brightness’. Unfortunately aluminium foil is reflective and just like with a visible camera the image would actually show reflected light (in this case infrared) and not show the temperature of the actual foil. This would confuse any meaningful analysis. So the inserted paper bowls enable us to measure the temperature of identical material surfaces in the same plane in both of the helmets. They were left like this for an hour to both acquire the ambient temperature. The thermal images at the bottom show that after an hour, in my un-air-conditioned living room, they were a balmy 33-34oC and within 0.3oC of each other.