Good day all.
Here is the test I promised , took a little longer then I expected as I did the test a few times to make sure my data was correct.
I wanted to do this test just to confirm to myself that the Internet
information about Polyiso (Polyisocyanurate)
losing its R value as it gets colder , as seen in this test.
This is not a scientific test so don't take it as the holly grail , this is just me doing a little test for my own and who ever would like to read it, information .
Basically what I did was take two outdoor RF temperature sensors , the same things you can buy at any hardware
store, encapsulate them in one inch of Polyiso and one inch of XPS or blueboard and through them in a deep freeze and log every 5 minutes the temperature changes. They were the only things in the freezer
and spaced equally from the walls .
I removed the foil from the middle layers of the Polyiso so not to get any thermal bridging through the foil but left it on the outside .
And of course the results.
As you can see these two insulation
materials are very similar in there performance with neither one being a clear winner . The Polyiso gives it up a bit to the XPS right at the 50 degree mark , similar to other test I have found on the net , but the warm up test made me scratch my head
a bit . No clear winner on warm up . As you can see I stopped measuring on the warm up past refrigeration
So my recommendation still stands , One inch of XPS on the cold side followed up by Polyiso for the remainder of the insulation
lay up schedule inside a box.
Please have a look at my results and chime in.