I will quote from the cover sheet that comes with Insul-Bright. "Not for use in the microwave." And: "The shinier metal looking side of Insul-Bright should always face the hot or cold item allowing it to reflect the energy back to its source."
(I will have to take issue the the "Cold" directions. If I have a lunch bag and want to keep my item cold, I would want to face the shiny side out to reflect the outside heat away from my lunch.)
But with ironing, you want the heat to be reflected back up to the item be ironed, so the shiny side should be facing up.