i am aware of a few companys that tryed this but none are around now,with a plywood floor you could put some insulation under the house,but not with a slab. a dense pad(1/2" 8lb) is as good as it gets....good luck

Thank you for the reply Carpetman!
Just FYI - I did happen to find something on the net after I posted this question. You can find it at: http://www.ghm57.dial.pipex.com/NEw%20site/Prod5.htm

I have written them an email with questions about using the products for my applications. I have an older home of poor construction that has mostly slab-on-grade floors, with a little wood frame flooring over unheated basement and am trying to cut the HVAC expenses.

So far it seems like there are more energy-conserving products being made/used overseas for some reason.

Thanks again, and Happy New Year! Nick