It should be the deluxe two layer version.
Smooth on the inside, in order to not scatter the reflected brain waves. You do not want to become confused.
Crumpled on the outside, in order that the hat is not detectable.
If you can achieve the magic 22.5 degree angle on the crumples, then there will be no emanations from the outside surface and since it is winter adsorbed radiation will convert to heat and keep the hat warmer.
My wife says to use the heavy duty foil, so the hat will last longer.