The thermal resistance of thin insulation

The thermal resistance of R'BULL thin insulation: does it really matter?

When someone asks us for the thermal resistance of our R'BULL thin insulation, it is worth pausing on what the letter R, so often quoted to judge an insulation product, actually stands for.

Before answering, we need to be clear about what thermal resistance measures.

What thermal resistance actually measures

Thermal resistance measures how well a material limits heat transfer. It plays a decisive part in keeping heat out of a home in summer and limiting heat loss to the outside in winter. Three parameters go into it:

• The thickness of the material
• Its thermal conductivity, lambda
• The surface area covered

In simplified form, the R value is calculated as follows:

R = thickness in metres / lambda

Take a 20 cm layer, that is 0.20 metre, with a thermal conductivity of 0.040: its R value comes to 5. The thicker the material, the higher its thermal resistance, which points to better insulation. A lower thermal resistance means the material insulates less well.

Beyond R: judging performance on other grounds

Asking for the R value of thin insulation makes little sense, because it leaves out most of what matters. Comparing thin insulation with a conventional product on thermal resistance alone is rather like judging an aircraft against a train on altitude.

Plenty of other factors come into judging an insulation product: speed, journey time, comfort, energy use, cost. The same applies here. Thermal resistance is mostly used to qualify for tax relief and for the energy performance certificate required when a home is sold or let.

When the priority is to keep the living space intact, thin insulation is the natural choice. Its low thickness simply calls for other criteria. In our next video we look at what else should be examined to judge an insulation product beyond its thickness.