Is thin insulation a good insulation solution?
You have probably already heard of the famous thin insulators, also called reflective insulators, multilayers… or some other trade name. Their thickness varies from 5 to 30 mm, which can be interesting for installations renovating inhabited attics. Their thermal performance is often given as equivalent to much greater thicknesses of classic mineral or natural wool type insulation. We can still read that a few mm are equivalent to 100 to 200 mm of conventional insulation! A statement that will surprise a good number of thermal engineers… yet thin insulation continues to be manufactured, sold and installed! So where does scientific reality lie?
Evaluation of the winter thermal performance of several thin insulators
- On which physical principles does a thin insulator work?
- What is their real effectiveness?
- How to optimize their pose?
- What is the maximum thermal efficiency that can be obtained with thin insulation?
- Equivalent to traditional insulation?
- Does the price guarantee performance?
You will find the answers to these questions in this thin insulation analysis and technical study by CSEC here is an extract from the conclusion ...
“During this study, the thermal performances of three thin reflective products (PMR) and of a traditional control insulator were determined during the winter period (…)
The thermal performances were measured on the various products in their initial state, that is to say as they were supplied by the manufacturers, and under ideal installation conditions (non-ventilated air space and constant thickness, etc.), that is, in the most favorable situation.
Given its low thickness, a PMR has a low intrinsic thermal resistance, the measured values varying from 0,2 to 0,6 m².K / W depending on the type of product. In order to benefit from the reflective effect of the surface layers, the product must be placed opposite one or, better still, two unventilated air spaces. Under these conditions, the emissivity value of the external faces of the product is an important parameter, which determines the reduction in heat transfer by radiation through the air space. The measured emissivity values range from 0,05 to 0,20.
The total thermal resistance measured of each product associated with two non-ventilated air spaces 20 mm thick varies from 1,0 to 1,7 m².K / W depending on the type of product and the direction of the heat flow which crosses. (…) "
Conclusion on thin insulation
Under the conditions of the BBRI study, an optimally installed thin insulation has, at best, a thermal resistance of 1.7 m².K / W. This thermal resistance corresponds to a conventional insulation thickness (lambda = 0.04) of 6.8 cm, i.e. 68 mm, therefore very far from the 200 mm announced and the air spaces must be perfectly made. It is also very far from thermal recommendations of the RT2005 which requires a thermal resistance of 6 to 6.5 for the inhabited attic!
In conclusion, if the performance of thin insulation alone is insufficient, even with 2 air spaces, the latter can appear as an interesting solution in complement (and only in addition) of a classic insulation.
In 2010, thin insulation alone cannot constitute an insulation with acceptable performance in our latitudes.
References for more information:
a) Download the study report on thin insulation by the BBRI
b) Insulate with a single air gap?
c) Tests by a particular on thin insulators