Yes, Insulbright has a right side and a wrong side. The shiny side goes towards the heat source in order to work. It reflects the heat back to the source that way.
Also, Elisabrat, if you mean you are using poly batting in potholders when you say "puffy fill", please be careful. Poly will melt if it gets too hot. Cotton batting is the best to use with insulbright in anything that will have close contact with heat.
Insulbright is also good to use for keeping things cold, so it is perfect for food carriers for hot or cold dishes. Again, shiny side faces the food dish. :D