In the Thermal Break thread, there was mention of Thermablok aerogel tape that the manufacturer claims can improve whole wall R-values by more than 40%.

I had pointed out that their website claim was based on the worst-case scenario of a 2×4 metal stud wall with R-13 fiberglass batts.

I corresponded with Thermablok and read through their test results on the downloadable CD.

These are the full findings:

Hot box tested R-value for ¼” gel: 10.14/inch (it comes 3/8″ but compresses to about ¼”)
Hot box tests on a 2×4 wood-framed wall with ½” open-cell foam and 3″ fiberglasss showed an improvement of 9% with the aerogel.
Hot box tests on a 2×4 steel-framed wall with R-13 fiberglasss showed an improvement of 29% with the aerogel. Additionally, it reduced temperature differences along the wall from 5.8° to 0.8°.
Hot box measurements performed on a through-fastened metal roof on a steel frame insulated with 5-in wide 3/ 8-in. thick aerogel strips, showed an increase in the overall roof R-value by about 14%.

According to the email sent to me by a factory rep, this is where the 40% claim came from:

“Calibrated Hot Box testing has taken place at the Johns Manville Technical Center to investigate the use of thin strips of flexible aerogel insulation as a thermal break material to improve the thermal performance of cavity insulated steel framed wall assemblies. The results of the testing showed that the aerogel insulation, along with an additional 3/8 inch thickness of JM Spider ¯, improved the overall wall system thermal performance by about 42% in comparison with a cavity insulated wall with no thermal break material installed.”

On their website, they failed to note that the “improved” wall also had more cavity insulation.