This may be way out in left field
 

DD has, to her utter astonishment, become a hockey Mom. Both DGD's are now playing. Weekends are spent in a cold arena. I would like to make her an arena cushion. I was wondering if I could use a double layer of the stuff you put in oven mitts put shiny side out, plus a couple of layers of batting between them, as the filler. Do you think it would actually reflect her own body heat back to her, as well as reflecting the cold concrete bench?

Having been a Hockey Grandmother, i would have loved that!!!

I think that would be nice, but they do make a really nice "seat" for hunting etc that you could make a quilted cover for... it is filled with polystyrene beads I think, and if you used the reflective stuff on the quilted cover, it would be wonderful. Be sure to add a carry handle to whatever you make as that makes it easy to take (along with her coffee, purse, kids stuff to be taking care of etc)

Many years ago, I worked in a plant where my seat at my machine was steel, which could be quite cold in the winter. Being a former Girl Scout, I made a "sit-upon" with fabric and stuffed it with fiberfill, using newspaper for insulation in it. If I had found something like Insulbrite, or something like that, I probably would have used that instead. Sounds like a great idea!