What is the U value of plexiglass?

Answer 1

Glass has an R value of approximately 0.14 per inch thickness

Celluloid (Lexan, Plexiglass?) has an R value of approximately 0.7 per inch thickness

[source: http://www.bobvila.com/wwwboard/messages/37235.html]

U value is the inverse of the R value. (U-value = 1/R-value)

Using this equation and the values above, the the U value of plexiglass is approximately 1.4 per inch of thickness. The U-value of glass is 7.0 per inch of thickness.

So, if these values are correct, then Plexiglas is approximately five times as resistant to heat transfer by conduction as glass.

I have seen this conclusion elsewhere a long time ago, but I have also seen values for plexiglass on a plastics dealer's web site that said the R-values of glass and plexiglass were approximately equal.

On another site, a value of 1.35 Btu*in/hr*ft^2*ºF

[source:

http://www.plasticsintl.com/sortable_materials.php?display=thermal&sort=thermal_conductivity]

There are some values given in SI units on other sites, generally consistent with the values given above.

Thermal conductivity of Acrylic sheet is listed as 0.2 (W·m−1·K−1) while glass is listed as having a range of values from 0.8 to 1.4, depending on the composition (0.8d−0.93e((96%SiO2)1.2-1.4g W-m−1·K−1)

[http://en.wikipedia.org/wiki/List_of_thermal_conductivities]

Again, then, the U value or thermal conductivity of plexiglass is given as between 1/4 and 1/7 that of glass.

More authoritative information and further discussion of this question would be greatly appreciated.