Relectix is well-known trick for getting a little more warmth out of your sleeping pad setup. The construction grade reflectix can be a little bulky however.
A quick, simple, light and very compact alternative is the reflective sun shields that can be bought in any auto parts store or auto parts section of a larger store such as Target.
Simply place the sun shield under your sleeping bag and/or pad setup (some people like the visor on top of the pads others like the visor underneath the pads) and get some precious reflected heat back in your winter setup. I suggest using a truck/SUV one as that size is larger and is a better fit for full-length sleeping pads. ( I’d eschew Mylar emergency blankets as they are thin and will not hold up to regular winter backpacking use.)
This article on the Hennesy Hammock page explains the concept in much more detail. (Scroll to the bottom)
So, if looking for a little more warmth for your winter camping, consider going to the auto parts store as well.
Not only for getting some essentials for winter safety while driving, but also for a quick camping trick, too. More durable than an emergency blanket if you winter backpack or camp on a regular basis, too.
Quick, simple, light, cheap: A sun shield. It works.
You may also be able to customize a size at your local hardware store, since they sell the raw material at mine!
Have you tested it yet? I’m planning on buying one for my camping next week.
I have used it on every winter backpacking trip I have done this season. As an aside, I only post “quick tips” I have used in the field. Have fun!