“I am assuming the 1.5" is the thickness. Is that measured from the bottom flat part of the mat to the tips of the peaks, or is it measured a different way? Also, how compact can you get it to pack with?”

Yep; bottom flat part to the peaks. I tried 1” mats and I noticed a big difference (I don’t like it). Or you can be like billk; he just uses an 2” open cell mat exclusively (with a home made cover).

My little extra pad rolls to 3” dia by 11”. One time, the tent I was in, leaked. The open cell pad didn’t absorb any water from the floor since it was on top of my protective thermarest.

-Barry