Ground insulation.

"Are the sol pads really that much warmer? I thought the reflective mylar thing was a myth"

There has to be an air gap next to the reflective layer

Like s space blanket on the outside with air above it

Or in a neo-air, the reflective layers are suspended inside so there are air layers against reflective layer inside the mattress

On the surface of a pad it doesn't do much – on one side of the reflective layer is the mattress – no air gap, and you're laying against the other side so there's no air gap.

I looked at the Cascade Designs/Thermarest website, to compare the a RidgeRest Sol to the Z-Lite Sol. The R value is slightly higher on the RidgeRest, 2.8 vs. 2.6. The weight on a Ridge Rest is ever so slightly lower too 400g vs. 410g, but you have to be a pretty serious gram weenie to get excited about 10g. :)

Note here that I’m comparing the most current versions of each, the “Sol” version with the reflective coatings. The difference between the two is 0.2 R.

HJ
Adventures in Stoving

But that aluminum rubs off. Decreasing R value, and generally being annoying.

I thought they disproved the head myth…

Anyways, the reflective coating definitely flaked off on my Z-rest. What I did not notice, once, ever, is a piece of aluminum dust on anything I own. I don't know where the coating went, but it delaminated in such a way as to be untraceable. I didn't find flakes in my tent or backpack.