REI and MEC will only sell sleeping pads with the new R rating.

I was specifically referring to air-only mattresses, where the density is the same, regardless of it’s thickness. Quite simply: unlike fiberglass batt, down, or open celled foam, air does not get more dense inside a compressed pad.

The air *is* the insulation in fiberglass batt, down, or open-cell foam insulation.  Air is a great insulator as long as you can keep it from moving, which is the job of the other materials.  Increasing the density of, say, fiberglass fibers makes the batt do a better job of stifling convective currents in the air.  There’s a limit, of course, beyond which further increasing the density causes conduction in the fibers themselves to short-circuit the air’s insulating ability.

Any air mattress with an R greater than about 1.0 has some fiberglass or other “stringy” insulation in it, and compressing that certainly does increase its density.  How much that matters is the open question.  I’d also like to know whether all the movement (for us rotisserie side sleepers) causes enough air movement inside the mattress to noticeably degrade the R.

I think have to remember the ways heat is transferred, in the case of mattresses away from our body.

1 Convection- air circulates within a mattress

2.Conduction- heat loss directly through a solid

3. Radiation- heat loss radiating out from an object (us or a mattress)

So an AIR mattress will lose most heat through Convection. 

A Closed Cell foam mat will lose heat through Conduction.

And both will lose some heat through Radiation.

An insulated air mattress will insulate against heat loss by: 1. reducing convection with fiber or down insulation (or, in the case of a Neo-Air, through layers of air channels) and 2. by reducing radiation using reflective interior coatings.

And yes, a self-inflating foam filled mattress reduces convection and conduction with foam, a great insulator but “heavy”.

In all cases good reflective coatings reduce radiation loss. Most mattresses use reflective coatings. I dunno if any self-inflating foam-filled mattresses use it.

In order for a reflective surface to work you have to have an air layer next to it

With a Neo air you could have the reflective layer inside with an air space on either side and it would work twice as good

If you put a space blanket under or over your matt it wouldn’t do much, no air layer so you don’t reduce radiant heat loss.  Having another layer of mylar would help a little, keep water out,…

There’s an emergency blanket with several reflective layers and elastic so there are several air layers next to reflective surface so that works even better