Dear Mr. Eugene,
Instead of us playing twenty questions and yapping back and forth about mylar, why don't you tell us where you plan on going and what you plan on doing where it is -40F, since you list your location as San Diego.

There are a couple of folks here that have experience in those temps (Alberta and Newfoundland) and can tell you what works and what doesn't.

Also, visit the winter camping section and look at those posts. There is one by TomD that lists another forum that is strictly dedicated to cold weather camping.

Tango61
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