Mylar for embroidery designs is not foil. That Mylar (foil) is the kind used to make the balloons.
Embroidery Mylar is a cellophane type material used for gift wrapping. It is ideal to use Mylar designs with it. BUT not completely necessary experiment. I know someone that tried an embossed design with very pretty results.
I posted a few links for you the first is a very informative site about Mylar.
The 2nd is a yahoo group that has some free samples of mylar designs.
Third more info.
Last link is for a couple more freebies in case you don't want to join a YG. Look for the 2 designs that have "all that glitters" in the title

The designs are specially made for Mylar. Less density on the top, so the mylar shines through.

Hi boo305

I have started a yahoo group dedicated to everything Mylar, I have a tutorial there also, Please feel free to come join and ask your questions. Thank you pssst for posting a link to my website. I felt it was time to start a Yahoo group as there are still so many questions being asked. I only started this group last night so have a lot to add to it, so please bear with me as I do that. I hope it will answer everyones questions about mylar.
Happy Stitching,
Sharon

Thank you Boo; *4u!

Here is another link to using Mylar.

Thanks you for asking and the peoplke that reacted thank you fo the info.

Hi, you need designs done ofr this time of material. the stitches can not be too close.