This defines a material's ability to transmit heat, being measured in watts per square metre of surface area for a temperature gradient of one kelvin (K) per unit thickness of one metre.

It is expressed as: W/m.K

It is both appropriate and convenient to measure insulation materials performance directly in terms of material's thermal resistance, which is obtained by dividing thickness (T) expressed in meters by thermal conductivity (λ) expressed in W/m.k:

       T
R = ---- 
       λ

It is expressed as m² .K/W


 

This defines a material's ability to transmit heat measured in watts per square metre of surface area for a temperature gradient of one kelvin (K) in terms of a SPECIFIC THICKNESS expressed in metre.

It is expressed as: W/m².K

It is to be noted that, where a structure incorporates a number of component materials, air spaces, etc, individual thermal conductance values cannot be added directly for a purpose of calculating an overall rate of heat transfer without the necessity for first deriving reciprocal values.

Thermal Conductance (C) and Thermal Resistance (R) are reciprocals of one another.

This defines the ability of an element of structure, consisting of given thicknesses of material, air spaces, etc, to transmit heat under steady state conditions.

It is a measure of the quantity of heat that will flow through unit area in unit time per unit difference of temperature of the individual environments between which the structure intervences.

This value can be obtained as reciprocal of sum of all the respective thermal resistances (R) of the component materials and the internal and external surfaces resistances:

                                    1
U       =     -------------------------------------------
                  R₁ +  R₂  +  R₃  + ......Rm

It is expressed as: W / m².K

For example, the following table shows the THERMAL RESISTANCE (R) of KIMMCO 12 & 48 kg/m³ insulation for each standard thickness at 25ΊC (77 ΊF), according to S.I. and IMPERIAL Units System.

 

                                              1
U  =   ------------------------------------------------------------------------------------
         Sum of the different elements' R value of the structure

RSO   =   External Surface Resistance RSI     =   Internal Surface Resistance R1      =   Facing bricks 5.5 cms R2      =   KIMMCO Buildingslab 5cm 48kg/m3 R3      =   Blocks work 15 cm R4      =   Plaster 1.5 cm

RSO and RSI depends on some climatic conditions (wind speeds for example) the thermal exchange ways (from top to bottom, the bottom to the top), if the wall to be insulated is vertical or horizontal.

The low thermal conductivity of fiberglass products is due to the fact that they consist of more than 95% air which is trapped and kept stationary by the thin fibers.

The dependencies of Thermal Conductivity of KIMMCO TEL process products on the mean temperature and density, according to BS 874, ASTM C177, C518 or DIN 52612 are presented in the tables below.

STANDARDS
COMPLIANCE 

Conversion Factors

Reference: ASTM E 380