Foam + air pad

[mstei4]

Not sure I can be sold a valid reason to not put closed cell down below. If r-values are cumulative, it wouldn't matter what was on top or bottom.

Benefits of the air mattress on top are both comfort and puncture resistance

Pads like the switchback and the z lite sol have a reflective layer designed to contain radiative heat transfer. Getting that layer closer to you will increase the efficiency (more coverage from radiative heat transfer leaks to the side and that reflection will be dealing with a higher source temperature [you as opposed to the air pad]. This is less effective with air pads that use reflective layers already (like the xlite) then pads with fluffy insulation (most every other air pad). That being said I usually put my foam pad under my air pad to get the protective benefits, usually something like gossamer gear thinlight or the mld goodnight, they’re 1/8” thick so are significant lighter and easier to pack than something like the switchback