In December 2011, I slept on frozen ground on the Edge Loop, above Fruita, Colorado. It was a mildly windy ridge with a little snow, but the ground was definitely frozen solid. Temps dropped to somewhere around 5F. I had a RayWay blanket with 2 layers of insulation, fleece pants, and slept in a Montbell synthetically insulated jacket. I used my handlebar pogies to keep my feet warm, and kept water in a Klean Kanteen so I could melt it over the fire in the morning.

For a ground pad, I used a 4' roll of Reflectix foil-bubblewrap found at Home Depot. I folded it in half, so it was effectively two layers of 2' wide insulation. I packed it like an accordion, and it took up a lot of handlebar space.

Results: It was plenty warm enough! The R-values vary depending on how it's used, but two layers would probably be a minimum of R6. I think one 4' layer of Reflectix would've been sufficient, but definitely put the pogies on your feet! They're really nice sleeping socks!

Reflectix pros: super warm, cheap, light, comfy

Cons: very large pack size

note: check out my RayWay tarp-tent; the ground was too frozen for stakes, but when I went to use rocks, most of the rocks were frozen from frost-heaving.. geeze.