The coldest bed I've slept in was a water bed with no heater. Those will sure suck the heat out of you. I was young and dumb back then, so I just kept sleeping on it.

I agree that you need a good pad, but I'd still get and use the Reflectix.

Just a few months ago I forgot my pad and slept on a piece on the ground. It was chilly, and hard and lumpy too, but I stayed warm enough.

Reflectix has no "R-Value", so how and why it works is sometimes misunderstood, but even when compressed the insulation in your bag provides the air space needed to retain warmth from the reflective material (as do the bubbles in the Reflectix material itself). I won't go into that anymore here, but I think it has a lot of qualities that make it a very good option for our usage.

I've spent a few nights in the 15º to 40º F temp range over the past few years and for me a piece of Reflectix has become essential gear. It can be the difference between being cold or not and any pad and bag can benefit from it (even the pad you forget).