Here is a link on how to use glitter flex. It appears to me that it is a product used for appliques, whereas mylar is used under a design to give it some shimmer .http://www.sewinspiredbybonnie.co...
I've also used the shiny inside of potato chip bags and the inside of those birthday helium balloons in place of mylar. Works fine.
They are not the same, however you can use it just like mylar.
I am not sure, but I bought a fabric called dress foil, and I have used that in place of mylar. Take a small design and test first. You can always turn the design into a key fob. Happy sewing
Thank you I was thinking of trying an applique design as well.We'll see what happens.