Best Performance / Cout ratio for the south of the france?

Best Performance / Cout ratio for the south of the france?

The purpose of this article is to present the main insulating and construction materials, to compare them. Above all, it should be borne in mind that the lower the lambda value λ (the ease of a material to let heat pass) is the lower the insulation material. Likewise, the higher the thermal resistance (noted R), the better the thermal performance.

  • Why and how do you isolate yourself ?
  • How to calculate the performance of an insulator ?
  • Overview of insulating materials
  • Insulating building materials
  • Construction materials without significant insulating power
  • Get the best price for his insulation work

Why and how do you isolate yourself ?

Why ? We know that insulation plays a major role in reducing the energy consumption of a building. More and more insulating materials are emerging, especially ecological materials. So let’s see how to compare them before presenting each material in detail.

How? ‘Or’ What ? The main insulation technique is to trap as much air as possible. Indeed, the conductivity of the air is very low (0.0262W / m².K) on one condition, however, that the air is as still as possible.

How to calculate the performance of an insulator ?

The performance of an insulation is measured as a function of the ability not to pass a (thermal) power through a surface. This is why, like an electric conductor, thermal insulation is characterized by a certain (thermal) conductivity. The thermal resistance, which therefore interests us, is calculated as follows:

R = e / λ
e: thickness of the material [m]
λ: thermal conductivity [W / (m.° C)]
R: thermal resistance [m²
.° C / W]


We want a thermal resistance R = 5 m².° C / W
What is the minimum thickness to set up ?

  • Glass wool, λ = 0.04 W / (m.° C)
    • R = e / λ
    • e = R * λ = 5 * 0.04 = 0.200 m
    • It takes a thickness of 20 cm
  • Sheep wool, λ = 0.035 W / (m.° C)
    • R = e / λ
    • e = R * λ = 5 * 0.035 = 0.175 m
    • It takes a thickness of 17.5 cm

So much for comparing insulating materials with each other. To compare two wall structures (insulator + carrier material + interior facing), you can go to the ubakus site. It allows you to compare the insulation of a complete wall (as well as the phase shift and the resistance to water vapor) by simply selecting the chosen materials and thicknesses. It’s fast, easy, free and efficient !

Overview of insulating materials

There are 3 main categories of insulation that have advantages and disadvantages.

Mineral wools: conventionally, it is glass wool and rock wool. They have a very good performance / price ratio and good fire resistance (suitable for wood heaters). However, their environmental balance is not very favorable (significant gray energy due to the melting of sand or rock and low rate of re-enclage). In addition, these wools are not very dense and offer a low phase shift and therefore a bad summer comfort (to be limited in the attic if possible).

Synthetic insulators derived from petrochemicals: these are polystyrene (expanded or extruded) and polyurethane. They are also inexpensive and offer excellent performance (out of place). They do not fear humidity at all, which makes them particularly suitable for external uses (external insulation). They also have good compressive strength (dall insulation). On the other hand, their very low density implies very low phase shift and poor summer comfort (no use in the attic). Their ecological balance is very unfavorable and the vapors released in the event of a fire are fatal.

Bio-smiled insulation: these are plant-based insulation (wooden wool, hemp, linen, cotton, cork, straw…), of animal origin (sheep wool, goose feathers) or from recycling (cellulose wad made from flyers, recycled textile made from old fabrics). The thermal performances are good and these insulation are generally quite dense (ideal in the attic for good summer comfort). They also allow a natural evacuation of water vapor (in particular plant-based insulation) and have the advantage of having a very favorable environmental balance. On the other hand, the price is often higher except for products resulting from recycling. As such, cellulose wadding is probably the best performance / price / summer / environmental comfort ratio.

Insulating materials, technical characteristics

We can distinguish 3 categories of insulation: those from minerals, those from petrochemicals and biosourced insulation.

Cellulose wadding :

Cellulose wadding is obtained from recycled paper which has received treatments to guarantee fire resistance, prevent the formation of mold and the arrival of rodents. Its composition makes it a biosourced insulator which combines high permeability with water vapor and good humidity regulation. However, it remains sensitive to compaction.

DisadvantagesPossible presence of an additive for flame retardant
Subject to compaction (including by its own weight)
Pulmonary inflammation possible during installation, use gloves and mask
Check out our insulating sheet dedicated to cellulose wadding to find out more.

Wood wool :

Wood wool, also called wood fiber, is obtained by defibrating wood scraps or otherwise untapped trees. It is appreciated for its strong contribution to summer comfort and for its hygroscopic qualities.

DisadvantagesSensitive to humidity
Must be treated against rodents
Must be fireproof
Is often coupled with 25% polyurethane to link the fibers together
Check out our insulating sheet dedicated to wood wool to find out more

Hemp wool :

This plant can be transformed into hemp wool, a biosourced insulator which combines high permeability with water vapor and humidity regulation.

Sheep wool :

After shearing the sheep, the wool is washed, untangled, combed, washed and finally shaped to reach the insulators sold. It is still possible to obtain raw sheep wool directly from a sheep farmer.

Expanded cork :

The bark of cork oak is taken every 8 to 10 years, in reasoned operation, to make caps, decoration and … insulation ! It is in its expanded form that it is most used in France; cork granules are steam heated to a temperature of 300 ° C, they double in size and agglomerate under the natural action of its resin, the suberine. But you can find loose cork to fill walls for example.

Linen wool

The fibers of the linen stems not used for textiles are assembled and thermoliated in most cases with polyester. It is therefore mainly found in the form of panels but also in bulk.

Coconut wool :

The coconut fiber is recovered from the outside of the coconut. These fibers are assembled to form flexible rollers or more rigid panels.

Glass wool :

Glass wool is obtained by melting sand and glass products. She traps inert air within her fibers which gives her strong insulating power.

Rock wool :

Rock wool comes from the melting of basalt (black stone of volcanic origin) or blast furnace slag (product created during the manufacture of cast iron) and has excellent fire resistance.

Exfoliated perlite :

Coming from a siliceous volcanic rock, the perlite is heated to almost 1200 ° C, which causes its expansion. It is most often found in bulk but also in the form of panels, associated with other elements.

Vermiculite :

As with perlite, vermiculite comes from a rock and under the effect of heat is considerably increased in volume. Very light, it is distributed in most cases in bulk but it is also found in the form of panels.

Polyurethane :

Polyurethane insulation is made from a foaming of polyols, methylene diisocyanate, blowing agents and additives. Its very strong insulating power means that polyurethane is sometimes qualified as “best thermal insulation”.

Extruded polystyrene :

Extruded polystyrene is an insulator from the petrochemical industry. Its strong insulating power makes it possible to significantly reduce the thickness to be implemented compared to a traditional insulator.

Insulating building materials

Please note, lambdas are generally higher with these materials but their thickness is much greater, which can give thermal resistances similar to a “classic” wall

Cellular concrete :

Cell concrete, also called siporex or thermopierre, is composed of sand (44%), lime (10%) and cement (3%) which are mixed with water (41%) to form a paste. This swells under the effect of aluminum powder (0.6%) which creates many cells trapping the air (hence the term “cell”). The dough is finally molded and then heated to 180 ° C to form solid blocks. In the end, inert air (which acts as an insulator) occupies 80% of the volume of a block of cellular concrete against 20% for the solid mass.

Hemp brick :

The hemp fiber (granulates of hemp fibers) is mixed in most cases with lime and water to form blocks to assemble for the manufacture of walls.

Monomur brick :

These are large blocks of terracotta bricks ensuring slight insulation.

Construction materials without significant insulating power

These are the traditional building materials which must be coupled with an insulating material

Raw earth brick (also called banco or adobe) :

Parpaing :

Cooked earth brick :

Get the best price for his insulation work

Different quotes should be made to precisely quantify your project and lower prices by competitive tendering.

Choice of professional: The use of an RGE (Recognized Environmental Guarantor) Qualibat craftsman is essential to benefit from the financial aid in force. This will also allow you to select a company that is evaluated regularly. Privilege professionals who travel to your home to carry out a specific technical study and do not sign the quotes BEFORE you have edited your financial aid files. Also observe the responsiveness of your interlocutor: is the craftsman available ? Take the trouble to call you back quickly ? Finally, require a certificate of ten-year insurance which covers the work carried out.

Analysis of quotes: If your current insulation is more than 10 years old, check that the quote provides for its withdrawal. It is possible that it took moisture in places, that the thermal bridges were not treated with caution, or that it moved over time. There is also the need to replace the vapor barrier, or to put one if there was none. Certainly this at a cost (transport and disposal), but you will have something lasting. Check that the proposed insulation level is sufficient to achieve interesting performances: R = 7 m².K / W minimum (compasses), R = 6 m².K / W minimum (rampants), R = 4 m².K / W minimum (walls). Finally, always take the time to reflect before committing.


Depending on your environmental requirements and your budgetary constraints, a wide choice of insulation is offered to you. Classically, with a limited budget, you will probably opt for glass wool which fulfills its role well in winter, even if summer comfort is not there. With equivalent thermal performance, cellulose wadding has a better environmental impact and a much better phase shift: it constitutes the best price quality ratio. To go further in terms of ecology, you can go to a 100% natural insulator like sheep wool or straw. Note that insulation works are eligible for the financial aid in force. Finally, an insulating material is often associated with a carrier material, consult our comparison of construction materials to find out more.

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