I live in Montana. "Montana" is a Mexican word for "mountain". You'll never guess why they picked this name.
I'm also cheap. "Evarts" is a Dutch last name and because nobody bothered to fight racism against Dutch-Americans, I've succumbed to the racial stereotype of my people being cheap. Hurtful terms like "Dutch Metal" and "Dutch Treat" broke my spirit and now I pinch pennies so hard electrons get knocked loose in my fingers.
Creativity prevails when hunting, mountains and cheap collide. One of the biggest challenges related to being in the mountains is temperature variance. Temperatures vary wildly and a 20-degree difference from one night to the next can occur year round. On a normal trip this means whichever sleeping bag you pack will be the wrong one roughly half the time.
I created these heat reflectors five years ago using free Low-E household insulation from my friend Patrick's remodel. I then cut them to size using a Therm-a-rest for a template. I cut them short to reduce weight. They are designed to reflect the heat of the torso mainly. I then trimmed them with Gorilla Tape to avoid fraying. They weigh 5 ounces and can be rolled up within the Therm-a-rest. There are versions of this reflective sleeping pad on the market that retail for under $20. The advantages of this one are; I know it lasts for years, it's free, it's a little lighter and I know it really reflects heat well. If you can't find the Low-E free from a remodel, Habitat for Humanity store or construction site you can buy a 125 foot by 4 foot roll for $181 and make a bunch of them and give away or sell the extras. A representative from Low-E suggested using "slab shield". So, if you're buying the product get the slab shield.
My family slept on these reflectors during hundreds of nights over the years. We use them in snow caves in the winter, sleeping on the ground in spring and fall and as a barrier to cold on our cots. Over the years we figured out that there are three heat settings with the reflectors. Low: Between he ground and the Thermarest. Medium: Between the Thermarest and the sleeping bag. High: Inside the sleeping bag.
Low-E is rocket science, but this reflector is not.