The white foam mesh that AC posted above is an idea for a 'spacer'.
Something to keep the reflective foil from being in contact with a conductive surface.
Alone, the mesh has little value as an insulator, or reflector. It's just one
component of a two part reflective system.
Since the space between my floor joyce planks is pretty deep, I think
the 16" wide Low-E tab product could be installed with staples,
in the middle of the joyce, leaving a lot of air space between the
reflector and the subflooring.
The main problems I see with the idea, about 1/2 my basement is finished,
with a lowered ceiling. (I would have to remove it).
And the unfinished area has plumbing and wiring between the joyces,
that I would like to keep accessible..
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The stuff that's under my vinyl siding is 3/8" foam sheet, with foil over it.
It keeps the walls from absorbing heat during the summer.
The heat radiated from the vinyl is reflected right back at the vinyl.
I have thin foil covered battens of fiber between the wall studs,
but the foil has deteriorated to a flat dull silver color since 1956
and is not very reflective anymore.
But, since the vinyl siding was placed over the old wooden shingles, that
were installed over a 1/2" fiber matting (over 1/2" planks)..
The over-all thickness of the walls helps keep the rate of loss pretty low.