Reynolds Release is aluminum foil that has been treated so food will not stick to it during the cooking (baking or grilling, etc.) process. It is relatively new --2 or 3 years???
WonderUnder is a fusible web product that you iron onto your fabric (I do it before I cut out my project) and then you iron it onto whatever you want to put it on. There is a paper backing that comes off before you bond it to whatever you are putting it on. There are a number of fusibles available now, but all work basically the same way.
Have a great quilting day. :-)