I used the ivory coloured Ensolite pads to well below zero back in the '70s and they were Ok, but, not up to Evazote; they would sometimes crack, but, that was more likely at -20*F and colder and few go out in such cold.
I have Ridgerest, MEC orange Evazote, forerunner of current yellow, Z-rest, GG Torsolite and Canadian Tire Roots Evazote, I much prefer the GGTL and this Can. Tire slightly softer Evazote to any of the others. It IS a heavier pad, but, I am at the age where such is worth packing and it works so well in real cold that I favour it for any cold camping.
My take on it is that the MEC yellow pads FEEL warmer than Ridgerests, which I have four of and do not care for, each to his own.
NOLS, I used my Paul Petzoldt Expedition Bag with an Ensolite pad I made by using pink plastic surgical strapping to fit together three layers of 1/8" Ensolite. I often used this at -20 to -25*F and it actually worked just fine. The bag was warm, but, very bulky and heavy.