Space Blanket to extend range of under quilt?

My only experience with a space blanket was using it for an unexpected overnight at 13,000 feet in thankfully good weather, 11 years ago. It ripped very easily. I hope the newer ones hold up better.

I’ve never tried it, so take this with a few grains of Morton’s Lite salt. I once tried using a close-cell foam pad instead of an underquilt, and woke up with my feet/calves all wet because the pad doesn’t breathe. I’m a warm sleeper, so no doubt that contributed. I think the same would have happened if I tried what you’re suggesting, but that may not apply to you. I’d probably want something breathable, and I don’t think space blankets are since I assume they work on the VBL principle (though, obviously, I could be wrong about that too).

space blankets aren’t breathable

in order for a reflective layer to work, there has to be an air space next to it

for example, if you put a space blanket on top of you, there’s an air space above, so it works

in a neoair mattress, the reflective layer is suspended inside the mattress so there’s an air layer on both sides of the reflective layer so it’s twice as effective

if you put a space blanket on top of you, and put a blanket on top of that, there’s no air layer next to the reflective layer so it isn’t very effective.  Maybe there will be some wrinkles so there will be a little bit of air space

I wouldn’t use it.  What temps are we talking here? A 30° under quilt would get me to about 25° .. I would layer more clothing to sleep in.. What’s your top quilt rated for? From what I hear, the under quilt protector can give you an extra 5 degrees warmth or so but I have never felt the need for one. Honestly, you may have to play around and experiment and see what works best for you.

Thank you all for your input. I can see now why the space blanket idea will not work.

I am talking about temps in the high 20s to low 30s.

My top quilt is rated at 20 degrees. I tend to be a cold sleeper. I will have extra clothes for the cold night temps so I hope that makes the difference.

I have also learned that I need to pay more careful attention to my UQ suspension to get the best performance.