Registered User
#1

I'm trying to work out how to convert thermal conductivity values to relative values.
I've tried Googling this to no avail.

If a product has a thermal conductivity of 0.037 W/mK, how do I convert this to an R-value?

Registered User
#2

10-10-20
I'm trying to work out how to convert thermal conductivity values to relative values.
I've tried Googling this to no avail.

If a product has a thermal conductivity of 0.037 W/mK, how do I convert this to an R-value?

The r-value is a thermal resistance,
The k-value is thermal conductivity = 1/r, usually W/mK

Registered User
#3

Ah for jasus sake!!

So, what if one company gives R ratings, and another just gives W/mK, how do I compare products?

Registered User
#4

10-10-20 .... If you compare two products that look very similar in spec with an identical thickness, can you see one with an an R value of approx 30 (27 to be exact) compared to another with a K value of 0.037 W/mK .....

If you can I have a formula ..... if not then I'm lost ....

Registered User
#6

W/mK is a measure of thermal conductivity, i.e. conductance per meter measured in Watts /meter * degree Kelvin. Resistivity, the resistance per meter is the inverse of this.

R is a measure of thermal resistance for the thickness of material concerned (for the example you gave 70mm, or 0.07m). Resistance = resistivity * thickness.

So 0.037 W/mK = (1 / 0.037) * 0.07 = 1.89 which is close to the R value quoted for the second example you gave.

So to convert from W/mK to R, take the inverse and multiply by the thickness in metres of the material you're comparing it to.

http://en.wikipedia.org/wiki/R-value_(insulation)

Registered User
#7

U value is strictly speaking measured in Watts per metre squared per degree Kelvin gradient. R value is the reverse of this. Alun has worked out an example for you