R'BULL, the insulation with a cloud effect

Why the image of a cloud

An overcast sky sends back towards the ground the infrared radiation the earth emits at night. That is why a cloudy night is milder than a clear one, at the same air temperature.

What the metaphor explains well

The cloud produces no heat. It merely sends back what rises, and that is exactly what a low emissivity face placed above a ceiling does: it does not heat, it prevents loss.

What the metaphor explains badly

A cloud needs no air gap, reflective insulation does. Without a still void in front of its bright face, the product conducts heat instead of sending it back, and the image then stops being accurate.

The mechanism in one sentence

Radiation is one of the three modes of heat transfer, along with conduction and convection. A reflector acts on the first, a closed air gap limits the third, and thickness acts on the second.

Why that mode counts more than people think

In a closed plenum a few centimetres deep, the air moves little and direct contact is limited. Radiation then becomes the dominant transfer path, which explains the effectiveness of a thin product in that precise configuration.

The limit to know

That reasoning holds for a closed plenum. In a solid wall or a cavity filled with material, the proportions change and thickness becomes decisive again, which takes nothing away from either.

Emissivity is developed on the dedicated page, and the conversion of transfer on the convection into radiation page.