Emissivity and thermal resistance of reflective thin insulation

Two quantities, two phenomena

Thermal resistance describes how hard it is for heat to cross a material by conduction. Emissivity describes a surface's ability to emit infrared radiation. The first is about thickness, the second is about surface condition. They are not comparable and they do not replace one another.

What a low emissivity says

A surface with an emissivity of 0.9, which is the case for paint or plaster, radiates almost everything it receives. A surface with an emissivity of 0.053 radiates almost none of it: it sends it back. That mechanism, not thickness, explains how a reflective product behaves under a roof in the sun.

How we measure it

The emissivity of R'BULL Pro 13 is measured to ISO 22097:2023 and declared at 0.053, with an S factor below 0.03. We publish the measured value rather than a rounded one: the normative rounding applies only below 0.05, which is not the case here.

The condition without which none of this works

Low emissivity only produces its effect facing an air gap. Pressed against a wall, an aluminium face reflects nothing at all: it conducts. That is the first cause of disappointment with these products, and it comes down to installation, not to the material.

Installation and the treatment of air gaps are set out on the page about fitting, and the product characteristics on the R'BULL Pro 13 page.

Why a measured value beats a claimed one

The emissivity of an aluminium face depends on its surface condition, and therefore on the quality of the film and of its protection. Two products that look alike can differ markedly on this point. That is why we publish a value measured in a laboratory, with its method, rather than a theoretical figure for the material.