Keeping the sandwich hot

 

Once upon a time before lockdown we went to see the snowdrops at the Bake Off garden. We had a lovely lunch with wonderful cakes. They served the hot sandwiches in foil lined bags. The shiny surface should reflect infra-red radiation from the sandwich back inside the bag so making it harder for the sandwich to lose thermal energy. I should have looked harder to see if the paper outer was attached to the foil. A slight air gap would have increased the insulating properties. Paper doesn't conduct as well as metal so it wouldn't be as hot to hold.