The "shiny" side of Insulbrite is the side with the mylar coating. Here's a picture of both sides. You can see that the mylar coating side is rolled into the bolt.
We sell quite a bit of Insulbrite and with each sale we include the following advisory, which is taken from the manufacturer:
Important Notes: When using in table runners or placemats, put the
silver side up. When using for potholders or oven mitts, put the silver
side toward the heat, and use an extra layer of cotton batting such as
Warm n’ Natural under the Insulbrite to provide additional protection
to hand or table. Insul-brite is heat-resistant, not heat-proof!
When machine quilting with Insul-Brite, your needles may wear more
quickly and may break. To prevent this from happening, quilt
SLOWER than usual and have spare needles available! Do NOT use in the microwave!
